What are the the relations, as written in the books, between the houses outside of the very clear enmity between Gryffindor and Slytherin?
For example:
As a whole what do the students of Gryffindor think about those in Hufflepuff?
Does Ravenclaw have the same very low opinion of Slytherin as Gryffindor has?
If the first match of the year in Quidditch is Hufflepuff versus Ravenclaw is there any trend among the other Houses about which they support?
From the Harry Potter Wikia article on Hogwarts Houses:
House rivalry is most seen between Slytherin and Gryffindor ("Gryffindor and Slytherin students loathed each other on principle" [HP6]). This rivalry likely goes back to the days of Godric Gryffindor and Salazar Slytherin after they founded Hogwarts, because the Sorting Hat said that they were the best of friends before they founded the school. [HP5] While it is not clear if there is a similar rivalry between Ravenclaw and Hufflepuff, it seems fairly unlikely due to the cheerful disposition of the Heads for said Houses, as opposed to the contempt of Professor Snape and the passion of Professor McGonagall. (Rowena Ravenclaw and Helga Hufflepuff, however, once great friends, are documented as having had a severe falling out at some point by the Sorting Hat's song in 1996.) It is sometimes thought that there is some dislike between the members of Ravenclaw and Hufflepuff due to the Ravenclaw students' reputation for boasting about their intelligence, which often annoys Hufflepuffs who are known for being modest, gentle and kind. As a whole, Gryffindors are thought to get on best with Hufflepuffs, whereas Ravenclaws are thought to be quite friendly with Slytherins. There are certain exceptions however, such as Harry's friendliness with Cho Chang and Luna Lovegood, both from Ravenclaw, as well as Cho's relationship with Cedric Diggory, who was from Hufflepuff.
Usually, though not always, the other two houses appear (in Harry's eyes) to support Gryffindor in its rivalry with Slytherin, which again is reminiscent of how Slytherin was in the end opposed by all three of the other founders. One exception to this occurred when Ravenclaw, Hufflepuff, and Slytherin all initially supported Hufflepuff's Cedric Diggory instead of Gryffindor's Harry Potter in the Triwizard Tournament. [HP4] Also in the first Quidditch match of 1996, it is said that many of the Hufflepuffs and Ravenclaws had "taken sides" in the Gryffindor vs Slytherin match, but does not specify which Houses took which side.
The books mainly portray the Gryffindor point of view, but additional information about the relationships between the Hogwarts houses can be extrapolated from Pottermore's "welcome messages" written by J. K. Rowling [1].
Open hostility from both sides:
Now, a lot of people say that Slytherins and Gryffindors represent two sides of the same coin. Personally, I think Gryffindors are nothing more than wannabe Slytherins. Mind you, some people say that Salazar Slytherin and Godric Gryffindor prized the same kinds of students, so perhaps we are more similar than we like to think. But that doesn’t mean that we cosy up with Gryffindors. They like beating us only slightly less than we like beating them.
Slytherin House welcome message
Generally on good terms, though Gryffindors consider some Ravenclaws weirdos, and Ravenclaws sometimes accuse Gryffindors of showing off:
But he had hoped the Ravenclaws might have found it in their hearts to support him as much as Cedric. He was wrong, however. Most Ravenclaws seemed to think that he had been desperate to earn himself a bit more fame by tricking the Goblet into accepting his name.
Harry Potter and the Goblet of Fire, Chapter 18 The Weighing of the Wands
The Gryffindors are OK. If I had a criticism, I’d say Gryffindors tend to be show-offs. They’re also much less tolerant than we are of people who are different; in fact, they’ve been known to make jokes about Ravenclaws.
Ravenclaw House welcome message
Very good relationship, even if Hufflepuffs are sometimes seen as "too ordinary":
The Hufflepuffs, who were usually on excellent terms with the Gryffindors, had turned remarkably cold towards the whole lot of them. [...] It was plain that the Hufflepuffs felt that Harry had stolen their champion's glory; a feeling exacerbated, perhaps, by the fact that Hufflepuff house very rarely got any glory, and that Cedric was one of the few who had ever given them any, having beaten Gryffindor once at Quidditch.
Harry Potter and the Goblet of Fire, Chapter 18 The Weighing of the Wands
Gryffindor (the house we get on best with)
Hufflepuff House welcome message
Slytherins are generally distrusted by Ravenclaws, who are in turn accused of being excessively competitive and bookish:
Well, you’ve probably heard about the Slytherins. They’re not all bad, but you’d do well to be on your guard until you know them well. They’ve got a long house tradition of doing whatever it takes to win – so watch out, especially in Quidditch matches and exams.
Ravenclaw House welcome message
We Slytherins look after our own – which is more than you can say for Ravenclaw. Apart from being the biggest bunch of swots you ever met, Ravenclaws are famous for clambering over each other to get good marks, whereas we Slytherins are brothers.
Slytherin House welcome message
Slytherins are extremely dismissive of the Hufflepuffs' lack of ambition; the Hufflepuffs share the other houses' negative opinion about the Slytherins:
Merlin was a Slytherin. Yes, Merlin himself, the most famous wizard in history! He learned all he knew in this very house! Do you want to follow in the footsteps of Merlin? Or would you rather sit at the old desk of that illustrious ex-Hufflepuff, Eglantine Puffett, inventor of the Self-Soaping Dishcloth?
Slytherin House welcome message
Of course, you’d expect Slytherin to churn out evil-doers, seeing as they’ve never heard of fair play and prefer cheating over hard work any day
Hufflepuff House welcome message
Ravenclaws openly appreciate the Hufflepuffs' niceness, but sometimes fail to appropriately recognize their achievements.
As for the Hufflepuffs, well, nobody could say they’re not nice people. In fact, they’re some of the nicest people in the school. Let’s just say you needn’t worry too much about them when it comes to competition at exam time.
Ravenclaw House welcome message
So, as you can see, we’ve produced more than our fair share of powerful, brilliant and daring witches and wizards, but, just because we don’t shout about it, we don’t get the credit we deserve. Ravenclaws, in particular, assume that any outstanding achiever must have come from their house.
Hufflepuff House welcome message
[1] Upon being sorted in a house, Pottermore users are shown a writing by J. K. Rowling in the form of a welcome message from the house prefect.
While, unfortunately, there are no official public links for the distinct messages, all four of them can be found from unofficial sources, for example in the Pottermore Wikia: Gryffindor, Slytherin, Ravenclaw, Hufflepuff.
Ravenclaws are often ok with the other houses although they are cautious of Slytherins because of their cunning (e.g. they might cheat in exams). Hufflepuffs are great but they are looked down upon by the other three. That's why they were so against Harry because he "stole" Cedric's glory.
Gryfindor and Slyterin are notoriously competative against each other, so aside from Slytherin they're cool with everyone.
Slytherin is sort of like the bullies of the school because of their drive to excel at everything, but they probably get along with Ravenclaws somewhat and just view Hufflepuffs as pushovers.
Ravenclaws are similar to both Gryfs and Slys but they have primary differences of interests so its logical to assume they'll get along with any house on a case-by-case basis.
Hufflepuffs are the rest of what doesn't fit into the other houses, so neutral. They more than likely get along with anyone who's willing to get along with them.
Those are based purely on sterotypes though. Any student can get along with any other student they want regardless of what house they're in.
Hufflepuffs I believe share common ground with all houses, maybe they get bullied a little by Slytherin as well, because they're quite friendly with Gryffindors themselves (i.e - Justin Flinch-Fletchy, Ernie Macmillon and Harry, Ron & Hermione)
Ravenclaws appear to be open-minded so I suspect they get along with Slytherins okay. Other than Gryffindor and Slytherin, I don't really see any other house rivalries in Hogwarts...well, if you count the Goblet of Fire, with the whole Cedric and Harry incident, then yeah, but other than that I'm sure there are no problems amongst those houses.
