Also, it is pretty much canon he'd be in Slytherin if he didn't choose Gryffindor.

He didn’t choose Gryffindor. He chose “not Slytherin.” So once he made his choice, Slytherin is the last place he would have ended up. Besides, the hat only wanted to put him in Slytherin because part of the heir of Slytherin’s soul was inside of him. Harry really doesn’t have any Slytherin traits. He isn’t particularly ambitious, and he always puts the needs of others ahead of his own.

Right, sorry, I meant if he didn't choose not to be in Slytherin.

Also, Harry does have Slytherin traits. He was highly ambitious with the horcruxes and on other occasions like finding Sirius in OOTP and is very determined and resourceful on multiple occasions, said even by Dumbledore when he questions the hat's suggestion.

Ambition tends to suggest that you want things for yourself. Harry only ever wanted to help others.

Icecreamdif, I meant the fans put Ron in Hufflepuff.

It doesn't matter where the fans put him, he's not in it

Ambition tends to suggest that you want things for yourself. Harry only ever wanted to help others. 

Ambition literally just means being hard-working towards goals, which is literally a trait Hufflepuffs and Slytherins share (except Slytherin's has a negative connotation because they were written as the villains).

Regarding Ron and Hufflepuff: I was going to say that the fans put Ron as his "second home" in Hufflepuff, which seems very strange to me considering his behavior which can be offensive and insulting in all kinds of cases (even though it's actually my favorite character because he's a real Gryffindor).

It's not that important to the discussion either, it was just a side note...

Regarding the ambition that you said exists in both Hufflepuff and Slytherin, it is true, but ambition is a very general trait, it can be the desire to be braver or smarter or more beautiful, etc. It is in every house in Gryffindor and Ribblanco too... In Slytherin it stands out Cunning and desire for power. (NB: You wrote that Slytherin has a negative connotation, you're right, they have a negative connotation and rightly so!! Think for a second, all the villains were in Slytherin, it's a house I'd also like to stay away from... If I were Rowling I wouldn't do that that Slytherin is the bad house, but what to do... this is what happened is canon, Slytherin if all the best to Slughorn and Leta Lestrange is a house that has been run over by bad people. What to do? Sad)

Ambition tends to suggest that you want things for yourself. Harry only ever wanted to help others.

It really is just a strong desire-who it's for doesn't matter-which Harry has had multiple times.

Ron is in Gryffindor by canon, I believe he should be in Hufflepuff, end of story.

Ambition is not a Hufflepuff trait, guys, that's hardworking. They can go together, but by definition it does not literally mean being hardworking toward goals, just having a strong desire to get to them, it doesn't always mean you work hard for it, but Slytherin's ambition seems to be in a negative connotation, like Draco's ambition to kill Dumbledore for Voldemort, who has an immense ambition to become immortal at all costs. Harry shows good ambition on multiple occasions, such as in DH on his plan to destroy the horcruxes and kill Voldemort.

Hufflepuffs aren't always kind at all times, so just because he gets mad on multiple occasions doesn't mean he isn't a Hufflepuff. He's loyal to Harry and Hermione, particularly Harry, best friends through and through it all, coming back after the Locket riled him up to leave them, and when he is loyal, he works hard to help them succeed. Yes, he does show some anti-Hufflepuff traits, like being the opposite of modest about Sirius Black attacking him with a knife, being impatient with Harry's lack of a plan, albeit the Locket brought out these traits, and not being a very hard worker in school, but I feel like he fits into Hufflepuff more than the other three houses.