So far for me:
Stock x with version 1 oem mod
Rpi v2 catless x with stock rear section (took it off after 48 hours. RASP)
Stock again for almost 2 years
Borla catless x with Borla Aggressive rear
Borla catless x with Gintani Sport double wall
I'm not done yet, still want to try other rear sections out. Not changing the Borla catless x pipe.
Stock is still my favorite. Excellent tone. No drone. Aggressive and pretty loud for a stock car. The sound this car makes from the factory goes by unappreciated.
Modified stock rear section was excellent. Loved it. But it was basically a heavy straight pipe set up.
Rpi version 2 catless x pipe with stock rear was bad. Loud as hell. 100% rasp 100% of the time. Sounded extraordinary at WFO but was not worth the insanely painful trade off.
Recently I went for a full Borla. It makes a lot of power. Sounds great. A little bassy but worth it. Some drone until you exceed 2000 rpm. Some inherited rasp from running no primary cats, but the sound is heard more inside the car than out.
As of a few days ago I changed the rear section out to a Gintani Sport. Sounds very similar to the full Borla but a little less boom and noise. A small amount more refined. I like it so far, it seems a bit quieter and that is ok with me. Also, I like the larger tips on the Gintani much more than the Borla tips. Big difference in the look of the car.
As far as power, the full Borla and Borla/Gintani set ups make the most all around power. The rpi lost a ton of bottom end. Made top end power, but it wasn't worth it. Racecar sounds at street racer expense.
Oem modded rear muffler made no difference in hp, as it shouldn't.