Carry what you shoot.
I agree with the idea of the carry gun be as close as possible to the one you shoot all of the time. I have 12 USPs (9 45s, 2 9mm Elites, 40 Combat.) I mostly shoot 45. I bought the 9s for cheaper practice and the 40 because it was too good a deal for $599 new. Several people have commented that they find the 40 too "snappy". I feel the same. Thats why I never became a 40 fan. If I want to shoot 180g ammo cranked up to 1100 fps., I can do that with a .45 and have the same result. I reminds me of my 44 AUTOMAG. My carry pistols are the same except the size. I have a .45 EXPERT and a .45 Compact. Both are V3 (no safety, with decocker) with loaded chamber indicators. I did this because too many times I found myself lining op a target and squeezing the trigger only to find that the safety was still on. I see this happen at the range all of the time. I don't want this to happen to me in a danger situation. Am I always going to remember to drop the safety? I'm not sure even after shooting several hundred thousand rounds. With the V3, I check the chamber indicator when I leave the house and I know all I have to do is pull the trigger. Both guns are MAGNAPORTED, ($140.00 each including shipping and insurance both ways) fiber optic front and rear sights, match triggers ( even the compact) and DECAL GRIPs. I can shoot the EXPERT a ton at the range and leave my COMPACT clean for carry. Both guns operate exactly the same. I don't have to think "which gun is this, what do I have to do differently than I usually do?" I don't know if this makes sense to anybody else, but it does to me.