assuming that you'll be using it in a studio, monitors should sound accurate (flat response) as possible. IMHO, no such thing as a genre-specific studio monitor. flat response is the priority so that you can make good judgement when editing your mix. if you pick one that is "pang hiphop" (pronounced bass and treble), you wont be able to make good judgement with editing.
first, plan a good room. then get a monitor that will have flat response in your room. if you want, get a good pair of flat response headphones (ex. the pro-audio line of Shure) para may baseline ka of what flat response should sound like.