The best depends on your taste. I like TRD because it gives a nice rumble without being too loud. Youtube haa plenty of exhaust vids.
As far as power and MPG goes...you won't notice anything.
That K&N is dyno proven to drop 5hp due to it not being a cold air. If you really want the best bang for your buck then buy a TRD blower. Anything else will get you little gains. You can change everything and almost spend blower money and not gain much.
I believe the TRD muffler is Bosal not Borla. Magnaflow usually aounds good on everything.
Bosal, that's right. Borlas are really loud. Yeah the Trd sounds pretty good. That's just alot of money for a cat back