While I have not owned any models in .357Sig, I have shot quite a few. I don't know what your preference as far as pistol brands and models go, but someone who was defensively-minded would be very well-armed with a G31 or G32, or a Sig P229, P226, or P239 chambered in .357. The most accurate and pleasant pistol that I have fired in the caliber was the Sig P226. This is a full-sized weapon, as is the G31, so if you are lookingtowards an open-carry only pistol, either would be a great choice. If you were looking for a pistol that could be used for both concealed and open carry, a mid-sized P229 would be a good choice (and the G32, too). For a strickly CCW piece in .357, it's hard to beat a P239. I hesitate to recommend the G33, as I have found it difficult to control during rapid fire, due to it's abreviated, two-finger grip.
The .357 Sig's recoil is like a very quick-recoiling .40. It has some snap to it, but the whole recoil impulse is over very quickly. The .45ACP, due to it's lower chamber pressures, has a significantly slower recoil impulse. It recoils more, but it's a smooth PUSH, instead of the Sig's quick SNAP. You will find that the Sig round delivers a very loud muzzle report as well. I am unaware of ANY subsonic rounds available for the .357 Sig, as that's kind of against the idea behind the cartridge, which is to be a blazing-fast 9mm. One thing that the .357 Sig doeshave going for it, is that you can fit more rounds into a smaller package than you could with the .45. Barrier penetration has been found to be very good with the Sig round, too, especially with bonded bullets like the Gold Dot.
I'd say, shoot both calibers in the pistols that you are interested in, and get the one you are most comfortable after that. I hope this helps!