Okay, so here's my unbiased input on the subject, I've owned a lot of polymer framed .45, nearly everything available in the country (HK45, USP 45, USP Tactical, USP Expert, MK 23, Glock 21 Gen 3 & 4, M&P 45 and so on) I've shot them all (I wont say intensively) but nonetheless. They are all great pistols, all have a little something that the other is lacking.
The only polymer frame .45 I have in the stable now is a G21 gen4. Why? It's the softest shooting .45 there is (okay, the huge MK 23 and the Expert were probably a tad smoother, never had both on the same range session...), and for the price, it simply doesn't get better than this. But, one things for sure, the G21 is softer on the recoil than the HK45, blame it on the lower bore axis, it does recoil softer and has less muzzle flip.
Finally, the HK45 is one heck of a pistol, is was a tad more accurate than the G21, from 15 to 25 yards that is, under 15 yards they were both equally accurate. If the HK45 was a $800-$900 pistol, that the spare parts, magazines and mods were affordable, it would still be in the safe right now. The reason is, who needs a $1500 service pistol who's spare mags are close to $100 a piece, extra parts are very close to unobtanium in Canada? (I know you HK fan boys will tell me that it's built like a tank and that it will never break...) For $1500 you can buy a great 1911, get a few extra high quality mags, have a custom trigger job and a few improvements that will simply blow the HK away... But hey, remember that I'm totally unbiased here, been there done that, you know the drill... And if we were allowed to CCW, it would be a different story... For paper punching, it just doesnt worth it.