Im lazy so usually type it hip-hop.
If Hip-Hop is the name of a form of music, then it shouldnt be capitalized. Rock 'n' roll isnt generally capitalzied in publications, its rock n roll or rock, neither is country music or pop music. R&B but that is because it is an abbreviation, thus rhyme and blues is not.
Having said that though I believe it should be capitalized, but for different reasons. Hip-Hop is a culture. As a culture it should be capitalized. Hip-hop music or rap does not need to be, but Hip-Hop culture does.