Your (and Pottermore's) opinion are all that matters! I'm definitely a Hufflepuff, I was sooooooooo terrified that Pottermore would sort me somewhere else but it didn't. So much relief. :)

Slytherin is one of those misunderstood houses, I think lots of people (who aren't as obsessive) don't want their friends to be in it because they think that means they're "bad" or whatever, but there are other qualities to Slytherin than just "bad" and "mean". Some of my best friends are Slytherins!