Anything that's well-written. Even if I chose a specific favorite type, if I read a badfic, I still won't like it as much as something that's well written in a genre I don't like.
But if I had to choose, I like writing crack fics (if it's just the plot that's crack and not the dialogue because I'm not particularly fond of random dialogue like "I like cheese"), dark fics (because they relieve stress), and science-fiction or fantasy.
Reading, meanwhile, I like anything, really. Basically, anything that wanders off the beaten paths a lot of other fics follow. The kinds that have plotlines that aren't just "new trainer goes off in new region," "characters fall in love," that kind of thing. Not that there's anything wrong with those, either.
