Couple thoughts. I've had both (a 6" Springfield 1911 that I ran .45 supers in, and many 10mms).
-.45 super is almost the same ballistics as .460 rowland without all the hassle, so is a better choice for most.
-HK USP is strong, but still not as strong as an all-steel 1911.
-Overall, I like 10mm more due to capacity and factory ammo availability (and more reloading data). But don't forget that you can get a RIA double-stack .45 super for less than $1K and make up for capacity somewhat. Both are excellent choices for big jobs (brownie defense), in my view.
-If you do go .45 super, I think another reason the 1911 is the best platform is that the extra weight will reduce muzzle flip, which is greater in .45 super than 10mm. Conversely, I think a polymer such as my XDM is a good match for the 10mm. Having said that, a 1911 in 10mm is also a very good choice, and will further reduce muzzle flip, making running hot / original 10mms still very fast to mag-dump; more so than a lighter polymer gun.
-Just to reiterate, in case there are beginners here, don't load .45 super loads in .45 acp brass. Brass must be marked .45 super.
-"Buy a 10mm, shoot a ton of .40 through it for practice, shoot and carry 10mm also. I've put several hundred .40 through my Glock model 40" - this is really unsafe due to ringing the cylinder and spiking pressures in 10. It's also a bad idea because you should "practice like you play", in my view.
-Don't forget the .50 GI if you like to go big. I *really* want one of those "double 1911s" but in .50 GI:
https://www.youtube.com/watch?v=XCOQf12y3kw
