Definitely Pinterest. If you're looking for stupid conservative memes, that's the place to find them.
I also don't like Twitter but I understand its purpose.
Quora is fucking awesome, but a lot of people get offended if you call it a social media platform. Although, I met a bunch of people there who I'm now friends with on facebook, so it meets the definition of social media as far as I'm concerned.
Facebook hands down because it doesn't do anything it offers well and is so massive. Instagram and Snapchat are very close though due to the fact the very function and purpose of them is retarded AF.