I've never fired a weapon but the design of Star Trek Phasers looks a little bit strange and uncomfortable to me (not the rifles though).
If we account for the no recoil effect of particle weapons and looking at the designs for Phasers for different eras of Star Trek, how easy would it be to hold and fire those phasers as compared with real fire arms of today? Does it resembles some kind of realistic approach or they are just made that way to look fancy?
Having been paid to shoot and teach shooting for several years...
As Tritium21 points out, very much about the way we handle projectile weapons is based on two things:
This is true in one way or another all the way from darts to throwing knives to javelins to atlatls to slings to bows to firearms to actual energy weapons in use today.
But a pure energy weapon has no recoil
The recovery time is whatever the recharge would entail. No idea what this winds up being in the Star Trek world, but we'll just assume its close to zero and they can shoot as much as they want... because, um... science. (That said, after personal experience with capacitor-driven microwave weapons, this could be significantly annoying.)
So that leaves us with #1, and that is mostly about lining up the shot and maintaining stability during the pull. In this case the "pull" will be a button press instead of a draw, swing or trigger-pull, but the weapons themselves appear to be incredibly lightweight -- which means either the triggers are really, really lightweight themselves (sort of scary, considering what the business end can do) or are incredibly well aligned with the natural motions of the fingers and the lines of tension exerted from whatever is defined as a "proper" grip.
This, by the way, is critical in pistol and rifle shooting. In fact, there are certain types of shooting where there is a direct parallel: slow-aimed-fire. Anything from match pistol, match rifle, Olympic-style bialthon (which uses a .22 cal weapon), benchrest and the new "lightgun" style used for the (ridiculously dumbed down modern rules of) pentathlon.
In all of these cases either a single shot is going out and it counts for everything, or the shooter is given a relatively huge amount of time to line up follow-on shots (so recoil isn't a factor aside from not hurting the shooter, as in the extreme range competitions where the guns kick a little harder than normal). The triggers on these weapons are as light as mechanics (or rules) permit, the grips are highly specialized to assist a shooter in locking the weapon to the body but with as little linear contact as possible, and the shooter assumes as stable a position as possible.
OTOH, close-range tactical shooting is rarely slow-aimed-fire. (Which is why the standard U.S. Army pistol test is not at all a reflection of combat competency but our old SFARTAETC "stress test", while still flawed, is much better -- and neither hold a candle to Bill Rogers' "reactive range" tests.)
Its all about body position
The importance of the stability of the firing position and grip cannot be understated because the trigger-pull itself is what will throw your shot. If you happen to have a laser pointer handy, turn it on, point it at a wall at least 10 feet away, and just see how steadily you can hold it on a 1-inch circle without doing anything else. Then try it sitting down. Then raise a knee sitting down and rest your hand on that. Then do it while breathing deeply. Then lay down and try it.
The magical answer to your question comes when you try the same exercise as above, but this time apply some stiff pressure from a finger into your grip. Try different fingers. Try pushing, sliding, pressing, yanking in different directions with different fingers, and watch what happens to your laser point (protip: it'll go totally wild most of the time).
To be even more accurate, put something similar to a Star Trek phaser -- like a TV remote -- in your hand and tape the laser pointer to it. See how steadily you can maintain your point of aim as you press buttons on it. This will tell you a lot about how practical the grip in the shows is.
My two cents
My suspicion is that its not a a good grip for an energy weapon unless they always lock the wrist bones down at the same angle and fully stress the ligaments on top, which sucks to do for more than a few seconds. I can't imagine that this would work out well in practice. Oh, did I mention, shoulder joints are inherently unstable...
Also, two hands always beats one; you can limit fundamental instability to just one dimension instead of three, and use opposing tension within a two-handed, cupped grip to stabilize the weapon as the trigger is pulled/button pressed/whatever. This is why gangsta-grip tends to result in a lot of sky-high fliers or ankle-level shots, even at very close range (for a right-hander they tend to be very high to the right or very low to the left -- but we're all quirky little snowflakes, which is why it is impossible to design "the perfect trigger/grip" pair).
...Unless they actually use a mental or voice activation we're not aware of. Or a button in the other hand. Or computer activation. Or... you get the idea. This would be totally badass and is the way to do high precision shots properly. But even then, its hard to hold a laser pointer at something very long with the confidence that you will destroy it (and only it) when the thing goes off when doing so with just one hand.
...Unless the energy weapon is itself somehow auto-aimed within a certain degree of accuracy. Considering we are trending toward modern weapons of this form today, I think its somewhat safe to retcon this aspect of mechanical assistance in accuracy into the Trek world.
EDIT: Something I failed to notice or mention initially, but grew curious about checking out a few Star Trek clips is that they appear to often be pointing the weapon with one hand and activating the trigger with the thumb. This is a terrible idea. The only reason we have triumphed over the other apes is our brains, but our further success over dolphins is due exclusively to our thumbs. There is only one on each hand. Without a very specialized grip that permits pressure from the metacarpal of the thumb to be the exclusive opposing retainer to all four gripping fingers (which is actually possible, but very tiring/cramp prone in practice -- srsly, try it), using a thumb to activate the trigger is almost a guarantee that you will throw your shot.
...and we'll just forget about those pesky aiming devices...
Something I did not address at all, but is absolutely critical, is the concept of "sight picture". There appear to be no sights on these things at all. Something the size of a TV remote can unhinge a bank vault door, but it apparently lacks a reliable aiming mechanism for all that power. Man, I sure hope these guys practice a lot, because they are always shooting from the hip. Shooting from the hip can be rather accurate though, out to about 25 yards. But beyond that the law of squares just eats you for lunch... (an inch off-target at 10m is how many inches off-target at 500m? You need sights on your scary-powerful energy weapon)
Unless the energy weapon is itself somehow auto-aimed within a certain degree of accuracy - I have a very vague recollection of this being mentioned somewhere
Having fired a weapon is not a prerequisite to answer this question. Shooting stance (with real firearms) aids in aiming and compensating for recoil. Phasers, on the other hand, have no recoil, and in some incarnations of the show, have targeting computers. But this is easy to test yourself, with a laser pointer.
If you hold a laser pointer in the same way that O'Brien is holding his in this picture, you get a clear view down the body of the weapon. If you press the laser pointer, you should (and I do, but I cannot create a video of myself to show this) hit whatever it is you are aiming at. It is relatively easy to aim such a weapon at close range.
This experiment does fail on one point, however. My laser pointer is a straight cylinder, not a banana shape. The banana shape of TNG and later era phasers make them MUCH more comfortable to hold and aim. Just hold our your arm in line with your eye, and your hand will naturally fall into a position to hold the weapon.
This is not to mention the various times in the run of the series when hand phasers have or have not had targeting aids. This would be a very comfortable, and possibly very accurate weapon.
Comparing to a modern handgun is a little tricky though. The only handgun I have fired is a Colt M1911 which, in my hands, has a little bit of a kick. The handhold is a little uncomfortable to me, but if the grip were in the position a TNG era phaser used, I am sure I would have broken my wrist.
There are no sights on phasers, but everyone assumes they are manually aimed. I don't see any reason why that's true.
Here's how it works, I think: you point it in the general direction you want to shoot, you look at the thing you want to shoot at, and a camera on the top of the phaser using sophisticated eye tracking technology determines what you're looking at. Another camera on the front of the phaser (dangerous end) takes a picture of the target area and using advanced image recognition, programmed rules, and what your eyes are looking at, it determines what you want to shoot at. It then projects a targeting beam at the spot that it's selected, which the shooter can see. If the spot's on the right target, the shooter presses the button. The phaser doesn't have to be pointed exactly right, because the emitter uses phased array technology to steer the beam towards the target.
At least that's how I always envisioned it working.
Edited to Add
From DS9: Return to Grace:
KIRA: This is a standard issue, Cardassian phase-disruptor rifle. It has a four point seven megajoule power capacity, three millisecond recharge two beam settings.
ZIYAL: How do you know so much about Cardassian weapons?
KIRA: We captured a lot of them during the occupation. It's a good weapon, solid, simple. You can drag it through the mud and it'll still fire. Now this. (Federation phaser rifle.) This is an entirely different animal. Federation standard issue. It's a little less powerful, but it's got a more options. Sixteen beam settings. Fully autonomous recharge, multiple target acquisition, gyro stabilised, the works. It's a little more complicated, so it's not as good a field weapon. Too many things can go wrong with it.
I think that indicates there's more to a phaser than simply shooting a beam where you point it.
Assuming energy weapons in the future have no recoil, holding them loosely is of no importance. Then again the actors were never trained in weapons utilization. Phasers were as much tools as they were weapons in the Star Trek series.
Also various episodes show that phasers had "auto targeting" though they still missed.
The phasers evolved over the progress of the series, resembling guns, then resembling wands tools. As the series progressed past TNG, proper hand holding of phasers and other weapons became more ergonomic for hands. Alien weapons on the other hand continued to resemble guns. There's no realistic way of holding a phaser, such technology doesn't exist but later models clearly showcase the weapon having black molded grips and continuing to curve to comfortably be held in the hand. Truthfully if I was designing a phaser I would study the ergonomics of prior firearms, where the defense industry spent years crafting firearms for adequate ergonomics. However NOT everyone in starfleet is Human so ergonomics must have given wave to practicality, a weapon that Any species in the Federation can hold adequately.
