So I've been thinking hard about this one and even though Hufflepuff is winning, I think he really isn't one.
The obvious reason is that he lacks the work ethic and is far from modest He would choose the spotlight instead of a quiet life any time wouldn't he? (thread) https://twitter.com/fanofshield/status/1290329586736287744

I feel like he does have some Hufflepuff traits, like caregiving, patience, loyalty plus he's not one to start a flight until provoked.
But I'm more leaning towards Slytherin (1st) and Ravenclaw (2nd), maybe hatstall level of closeness. +

As arguments for Slytherin: I think he's very resourceful & ambitious, he'll also often do morally questionable things in order to get what he wants (which is mostly recognition/ respect/ fame). Look at his trademark of appropriating other people's work to his own advantage +

(that SCREAMS Lockhart to me, a Ravenclaw who has a lot of slytherin in him, imo).
He's obviously super clever and eccentric, he really appreciates & accepts quirky people - that's so Ravenclaw! +

I think might just lean more towards Slytherin because he would never leave his own
friends/family behind, I think he'll do whatever it takes to protect them, really values them above all else.

What do you guys think? @luxromanoff @WillankaMH @wwwdotnope