The Amuse single titan has the highest proven dyno number, and sounds great. I personally have the JIC Magic bullet exhaust (the SS/Ti hybrid), and I love it. Without silencer, the exhaust has a high dB output, but you will get used to that soon enough...
Power: Amuse single
Rarity factor: C-West, Top Secret, any underground JDM tuning comp.
Least loud: Mugen dual (also has very small gain, if any), or Comptech
Go single in my opinion. It is the most proven style for HP gain.