Gryphon of course. Waiting on my custom tune. I have the K&N intake and I didn't find out about the the Gotts mod until a couple months after I got my intake. I was pissed when I read about the Gotts mod because it is so easy and only a fraction of the cost of an intake. Oh well, I love the sound of it though. I also cut out my muffler and tailpipe and put in a 12" Dynomax Bullet straight through race muffler and 45d it in front of the rear tire. Sounds awesome. Loud, deep and no crackling or popping and I still have stock cats. Muffler was only $40 so that was a cheap upgrade.
YouTube - F150 Bullet exhaust