I think your best bet is to find things that interest you. What are your hobbies or passions? I think you probably can be successful in any niche that is interesting to you as long as it is interesting to others as well. Be as specific as possible though. Good luck!
it really only matters what you like and something you can market effectively I personally have many different niches
Rule #1 of affiliate marketing : Never reveal your money making niches to anyone. I hope you understand.