Hans: My absolute favourite thing about Hans (other than his charming personality and dreamy eyes) is that according to the Disney Wiki, he was based on the magic mirror from the original tale (which I thought was positively INGENIOUS) and that he was able to adapt his personality to best fit the situation based on the person he was interacting with. If that isn't cunning, nothing is. And Slytherins are the "crafty, cunning" house. I don't know if I need to expand further on Hans, because practically every facet of his personality seeps with Slytherin traits, both negative and positive. He's not in Slytherin "because he's the villain". He's in Slytherin because of his personality. I don't believe in villainizing Slytherins--in fact, I think that Gryffindors have just as much potential to act out of evil as the Slyths. But Hans...is a Slytherin through and through.
Elsa: I had a lot of trouble sorting her, to be honest. What it came down to was my personal interpretation of how she handles her powers. I felt that Elsa spent so much time secluded because she was trying to learn to control the power, albeit out of fear of harming her sister, but she felt it was the most important thing to learn none-the-less. One quote from the post above that I found particularly relevant was "Ravenclaws have no time for stupidity or ignorance, particularly the latter." For me, this reflected in the scene after her coronation when Hans and Anna ask for her blessing. I feel like Elsa was upset by it because Anna was acting irrationally and being ignorant when she tried to make her see sense, which is what really started the whole problem in the first place. She has no problem being on her own (whether or not she prefers it, is less of a factor here) and after being cooped up most of her life, it's no far stretch to think that she'd be rather introverted with deep thoughts and most likely, a love for learning through the comfort books allowed.
***For both Anna and Kristoff, let me say that just because I sorted them into Hufflepuff does NOT mean I don't think they're brave. Gryffindors are not the only people capable of bravery and one case to expound on this point is Cedric Diggory. I mean, come on guys, without Cedric, Harry would NEVER have figured out the riddle of the egg on his own. One thing that bothers me is that many people use the excuse, "They don't do much" or "They're underdeveloped as a character" to explain why they believe someone should be a Hufflepuff but--that is NOT the case here. I have great respect for Hufflepuffs and if I classify someone in their house, it's not without first thinking it out and weighing every option.
Anna: The entire movie is pretty much about Anna's unending loyalty to her sister. Elsa freaks out at her party and freezes the entire kingdom? "My sister's not a monster." Elsa runs away to the mountains and barricades herself in an icy fortress? "We can work this out together." I think it's absolutely admirable how much faith she puts in Elsa, how much love she holds for her and how much she trusts her despite the fact that they've been estranged for so long. She longs for the friendship they had as they were children, and she has no ulterior motives for feeling so. To quote the post, "being alone or feeling unloved are things Puffs dislike intensely", which is a big part of Anna's character. It's the reason she's so hopeful for Elsa and her relationship to heal, it's the reason she's so excited by the prospect of her new relationship with Hans and even why she's willing to jump headfirst into their love story. I'm definitely not saying that she lacks bravery in the least--she's absolutely very brave and thinks on her feet, much like a Gryffindor does. But in the end, I feel her Hufflepuff attributes encompass her much more deeply and all inclusively than those of a Gryffindor, though I definitely see many of both houses in her personality.
Kristoff: Straight up, the sorting hat says "Hufflepuffs are loyal and unafraid of toil". The kid's out there constantly chopping ice on lakes in the mountain and if that's not hard work, then I can't really think of what is. The song "Fixer Upper" towards the end of the movie, I believe, was the most complete tool in decoding Kristoff's personality (and I just thought it was the most adorable thing in the world). He adores Sven and cares deeply for him and his family who took him in when he had nothing and even though he's living with a valley of rocks, he doesn't care at all because he LOVES them and they love him back and really, that's good enough for him. (I have a theory that the parts of his childhood they did not show in the movie must have been bordering on depressing or even dark, and that perhaps that is what made him lose his faith in the majority of humanity, at least as longtime companions.) Quote, "They're the sort who'd rather do something safe and reliable than flashy but risky" and that's definitely a Kristoff attribute. Hufflepuffs are really just the epitome of human decency and though Kristoff may try to hide it, I believe that on the inside that's him to a 'T'. Once again, I can definitely see many Gryffindor qualities in him, but when it came down to it, I believed he was better suited as a Hufflepuff.