They're both Glocks, so you really can't go wrong either way. You can have both calibers (.357sig and .40S&W) in either pistol, so it pretty much just boils down to what you want stamped on the slide.
I was recently looking to get into .357 Sig. I decided to buy used rather than new, and was looking for a 33. Found one that also included a lone wolf .40S&W barrel. I like the smaller profile of the 33.
If you're also looking to have a 9mm conversion barrel, I'd also suggest that you consider replacing a couple other internal parts just to make it more reliable. A 9mm recoil spring, and 9mm ejector could prove helpful.