Outside of the military, I have taken commercial firearms training courses at both the SIGARMS Academy in New Hampshire (now called the SIG SAUER Academy) and at FrontSight in Nevada.
My experience at SIG consisted of a 3-day Concealed Carry Pistol course. They have a great indoor range where they shoot only lead-free frangible ammo, which means you can get up close with the reactive metal targets.
At FrontSight you generally have to contend with outdoor courses where you are exposed to all of the rigors of weather in the Nevada desert. In return you get access to some very long ranges and simulators. My first experience at FrontSight began with a promotional half-day submachine gun course. Subsequently I have done one-day assault rifle and shotgun courses, as well as a two-day practical rifle course. In every case I drove up each day from Las Vegas. My best experience was with the one-day courses, which you can custom schedule almost anytime one of the longer courses isn’t in session: My wife and I had an instructor and a range to ourselves, and all ammunition was provided. List prices for Front Sight can seem very high, but the institute’s director, Ignatius Piazza, is constantly running promotions so I would be surprised if anyone pays full tuition. You can usually find discounted course “certificates” that cover tuition on Ebay.
The single most important variable in your experience at either institute will be your instructor. On the whole I have been quite satisfied, though not every instructor is equally engaging or capable of adapting the content and pace of instruction to the students. Both institutions keep a decent instructor/student ratio, so incompetent students tend not to bog things down. One other thing you have to deal with at Front Sight is Ignatius Piazza’s cult of personality: Classroom time will include details of his personal philosophies as well as extended pitches for you to buy Front Sight membership and more courses.