For me, it depends on what I want to do with it. For just plain fun shooting and plinking with any 22 rimfire ammo, it's hard to beat the Single-Six. For rough carry and "don't know what I'll be shooting" I carry a Taurus 94 stainless with rubber grips. A DA is just easier to reload than a SA and (I think, anyway) more rugged than an auto. If I'm hunting tree rats or wabbits, I take the Mk II. It'll only shoot long rifle ammo, but it's like a little rifle with Mini-Mags.
Lots of help, huh?? I just like 22 rimfire handguns, so I guess which one to take at any particular time is more of a preference thing than a hard fast rule. I guess that if I have to take just one, I'd be very sad, but it would be the Mk II.