I can see an argument for Hitman. Dude, outside of the Conceited battle (where he still one of the greatest first rounds ever) has a memorable performance every time.
My Top 5 changes so often, because you can't really make an "of all time" list, way too many different eras and levels of consistency. People I would have considered top of the game in the GT era are bums today.
ATM:
Hollow Da Don - Most well rounded of any battle rapper, just put a beating on Lux, his worst performance vs. Verb is still flames and has some of the most memorable rebuttals ever
Charlie Clips - Also very well rounded, consistent murdering spree, only real flaw is laziness
B Magic - More consistent than any other battle rapper
Danny Myers - Very consistent, has been on a murdering spree, even the vets acknowledge him as a threat and are willing to battle him
Pat Stay - Also very well-rounded, just needs to be challenged a bit more
I'm looking forward to seeing more Ty Law, Mr. Mill$, Sno, Charron, Real Deal and LottaZay. The first 3 because they're also some of the best out of the new PG classes, Real Deal because it seems like he's finally getting better and more matches now that he's a part of Dot Mobb, and LottaZay because he's been in the game way too long and is way too talented to be getting all of these shitty match ups.