"What if you weren't in Slytherin? Which other house would you be in? And what would you do?"

Hello Holly,

If I wasn't in Slytherin (which is almost painful to imagine) I would most definitely not be Salazar Slytherin's heir, therefore would never have been able to speak parseltongue nor would I have found and opened the Chamber of Secrets. Again, hard to imagine.

If not in Slytherin, I would most likely be a Ravenclaw, since I am above intelligent, in more ways than one.
I am top of the class, model student, prefect, head boy, etc.

As for your last question, I certainly wouldn't have opened the Chamber of Secrets, created the Death Eaters, learned about horcruxes or got into dark magic. I would've been a very different person.

Yours,
Tom Riddle.