I'm a recoil junkie
I must love my Ruger Redhawk .44, because I somehow end up taking it on almost every range trip. I reload for it, which is the only way to afford to shoot it.
I usually load for max recoil, 240 gr LSWC and WC820 surplus powder (cheap but so much smoke I've had folks think I was shooting Black Powder!).
I've shot .50 AE from the Desert Eagle. Now *that's* an awkwardly bulky pistol! But fun. Gas-operated semi action seemed to soften the blow a bit.
I've shot .500 S&W, and was almost disappointed that it didn't hurt. Kind of anticlimatic, given all the hype. Yes, full factory loads in an unported gun.
The most *painful* one-handed recoil I've felt was 12 ga Winchester 2oz Turkey loads, from my Serbu Super-Shorty. That was with the original plastic grip. I shot it once, figured I had bruised my palm, then shot it again just to make sure. I've since changed to an almost ridiculously soft grip, but it works great. Any other 12ga loads are violent, but not in any way painful.
I've also fired pistol-gripped riot shotguns one-handed (once with one in each hand), and the extra weight (and shift of center of gravity) counters the higher muzzle energy from full 18" barrels.
The platform has everything to do with it. For instance, here I am shooting an AA12 full-auto shotgun one-handed:
http://members.aol.com/fiftyguy/AA12_FIFTYGUY.jpg
...which was utterly controllable and painless.
Now, lest some of you think I'm being all "macho", let me say this: I've found many "lesser" calibers to be VERY painful to shoot from smaller platforms. I DO NOT like shooting .380 from Walther PPK's - the gun is just too small and awkward to grip in my hand, and the round makes for an uncomfortable level of recoil. Same with .357 Magnums - to me, there's usually not enough gun there to absorb the recoil.
I also like my CZ-52. But until I ground down the trigger guard and frontstrap to fit my hand it was unpleasant. It's got .357 energy, but with a fast, light bullet that makes for less recoil.
I imagine even a .22 derringer or pengun could be plenty uncomfortable to shoot.