Genre-wise, romance and historical. The first because I personally find it quite dull to read (but I can appreciate there are some books classed as romances which are probably well-written - I just can't get past the love-interest element). Historical, as other people have said, would require far too much research and, while I love researching for non-fiction, I don't think I'd enjoy mixing it into fiction writing. I'd also be too worried about getting it wrong.
Content-wise, abuse of any kind - but especially animal abuse. It had never crossed my mind to write about that until I saw people mentioning it in this thread. The idea is just too upsetting. Things like physical and mental abuse are also kind of disturbing.
But saying that, I will write about violence, so I'm thinking it's the psychological aspect of abuse I find really off-putting to write about.