Everything goes as long as you're feelin it. Sample from everything you like. I don't mean to disrespect OP, but this question pops up every once in a while and I think it's kinda stupid. One of the things that will distinguish you from other producers is the type of samples that you use, so there's really not a BETTER genre to sample. Just sample what you like and make it sound ill. Plus I believe that almost everything is flipable, if you can't flip it properly you can bet that there's some cat out there who can. So really, just find some bands and genres that you like and start from there - research related bands and genres, and so on and so on.