Clint Smith/Thunder Ranch is my first choice. Clint is just amazing as an instructor and Thunder Ranch has great facilities.
I wouldn't focus all of my tra
ining time with any one instructor though. Everyone has something to offer. And you will be better rounded, having trained under a number of different instructors.
John Farnum/DTI is another of the gods in the firearms training world.
Louis Awerbuck also is in the Pantheon of gunfighting instructor gods too.
And don't become 'gun-centric'. Take classes in knife and unarmed fighting too. Mike Janich is very highly regarded.
And for a full understanding of the entirety of the dynamics of a lethal engagement, I recommend Mas Ayoob's LFI I class at Lethal Force Institure.
Eastern thought meets Western GunFighting