Lets look at the profile of each:

Rockers :- Said to be the fruit of the gods, brought down to earth to save humanity with violence, drinking and music so loud, you swore it came from the deepest depths of hell. Some rockers tend to have hair that they use to wrap around the necks of their enemies and break them like twigs. The most common weapon is the guitar, either used to smash non-rockers over the head or to deafen their enemies with. Legends. Also use their head, fists and legs to cause maximum damage, drink in-human amounts of alcohol.

SPECIAL ATTACK: Head butt of oblivion.

Rappers :- Other than the fact that they are annoying, not much is known about them. Poorly said rhymes are said to be confuse anyone who they aren't fond of, giving them enough time to wimp out and use a gun like a wimp instead of their bare hands. Some are said to use their long chains to choke someone, by wrapping the chain around necks and pulling tight.

SPECIAL ATTACK: Bling Whip of doom

It seems pretty even! Who would win? Its hard to tell.