Depends what you mean by best? Best quality? Best sound? Best gains? Best value for money?
There's a good few options though. Mongoose or Scorpion do a system for the RT I believe, as do Ashley Competition, you could get a custom Powerflow one made up also, or get a Piper exhaust.
Loudest + Best value for money is the Ashley as it's mild steel. Good build is Scorpion imo. I've not been a fan of the Piper exhaust (not the make, just the sound). And obviously Powerflow suited to your requirements so best of everything. K-Tec are ok, but I heard some people have fitting problems and knocking problems... not many but one or two!