You can't go wrong with the #2 size trap. This is particularly true if you're trapping in winter conditions and trying to keep traps running with waxed dirt. You just use way less with a #2 size than you do if you go bigger. I like a 4 coiled Bridger with a dog and laminated jaws. Nothing wrong with the Duke and MB 550 traps or the No BS Jr. - I just don't see a reason to spend the extra money when the Northwoods square jaw design is pretty much perfect. If you were trapping in the SW, the bigger traps would definitely be the way to go. I use both the Duke 650 and the Bridger/Northwoods #2 traps. Both work great here, but it's easier to keep the smaller traps going in freeze-thaw conditions.
