Shop around and buy what you want.
Myself I've got an Armalite, a Colt bastardized 9mm, and a PWA. They all go bang when you pull the trigger and I'd swap all the parts around if I had to.
Bushie- good track record, supplied some M4's to US military once upon a time
RRA- good quality, won DEA contract. Receivers are made and machined by Stag (I don't care what Questar tries to tell you.)
Stag- CMT supplies parts to a lot of the major manufacturers (including Colt). Best bang for the buck, closest to mil spec you can get.
You could just have a rifle put together for you. Pick the parts and components that you like from each manufacturer and build your ideal gun.
As for stainless vs. chrome lined. Chances are that you could not afford the amount of ammo and range time required to burn out either of them. My advice would be to go with stainless. It won't rust,and it has better accuracy. It has all the advantages of chrome lined without any of the disadvantages and is normally available in 1/8 or 1/7 if you want to shoot some of the heavier stuff.
Good luck with search and keep us posted