Between the usual players, Data, Riker, Worf, or other occasional people to visit their table, how do they compare? Riker seems like the stock person to fulfil the card-sharp role, but I seem to recall him being occasionally trounced as it would be too predictable.
If you mean, the luckiest, TVTropes has this to say:
Whenever a poker game is shown in Star Trek: The Next Generation, you can bet that Riker will always turn out with a possible straight that he's bluffing about. Whether or not the bluff is called, though, depends on which would be more dramatically convenient.
If you mean, the best player, Riker again.
This article quotes Picard from "The Price" episode:
“Commander Riker conducts master classes in poker,” explains Picard.
As a nice illustration, see the game in "All Good Things...", after which Worf asks of Riker:
“Four hands in a row, how does he do it?”
If you mean can theoretically be the best player if he used 100% his full abilities, it would possibly be LaForge.
In “Ethics”, he admits to being capable of reading everyone's cards with his "Visual Instrument and Sensory Organ Replacement" (VISOR), though he claims he never actually uses that ability in their competitive games.
Riker, Geordi, Troi, and Data all have bonuses going for them:
- Riker is great at bluffing, and has rather good luck
- Geordi could see through the back of the cards
- Troi is an empath, and can generally tell when someone is bluffing
- Data has memorized an immense number of games and can easily calculate probabilities
But they also tend to check and balance each other in various ways:
- Troi can't read Data
- Data starts out unable to tell if anyone's bluffing, but gets better as the series goes on
- They usually play with cards that have a special backing that Geordi can't see through (said to Worf after a game once)
- Troi and Riker were once quite close, and still retain the empathic link - she can almost certainly tell when he is bluffing, even if she has some difficulty with the others
Data seems the most able to fill that role given that he is shown to clean house with the players in "Time's Arrow". He mentions at some point during the series that he initially memorized virtually every book on the subject but found that the actual game was different than the mere "book" knowledge. Given that he can simulate games in his head with actual data culled from past games as well as being able to precisely recall each player's appearance or gestures at any given moment and weight that against the numerical performance of that player and the game as a whole.