I voted .45ACP. The gun and cartridge were literally made for each other, and to this day I think the 1911 is still the best and most efficient launch vehicle for .45ACP, especially the lightweight Commanders.
For a long time I've wanted a 5" all-steel .38 Super to play with, but truth to tell I have no need and no real use for one and have a hard time justifying that kind of whipout for an expensive toy shooting expensive ammo.
I think the 1911 is a marginal gun for the 10mm cartridge, though I can see the appeal if one wanted a fairly packable defensive handgun in "bear country" or something of that nature.
In both 9mm and .40, there are more efficient launch vehicles than the 1911 that I like better.
The 1911 makes a lovely .22LR platform. I've put around 25K rounds through a Colt Conversion unit (Service Ace type), a carefully logged 15K+ through a 5" Ciener unit, and I don't even know how many thousands of rounds through a Ciener Commander-length unit. Shooting the 1911 is twice as much fun if you're not worrying about the cost of ammo, nor accounting for every single piece of brass. The 1911 with the 5" Ciener in semi-permanent residence on it is one of my to "go-to" grab-it-and-go-and-don't-worry-about-it .22 plinking handguns, the other one being a 4" S&W M17 K-22.