I have a SingleSix with both cylinders, and a Mk I 5.5" bull barrel.
The revolver is a ball to shoot, and I love having the option for everything from .22 Short up to .22 Mag. It has fixed open sights, and is quite accurate, the magnum cylinder seems a little more accurate, probably because the bullets fit the barrel better. Yes, there is a slight difference in bullet diameter between LR and WMR bullets. I've killed many rabbits and squirrels with it.
The old MkI, on the other hand is LOTS more accurate than either of my 10/22s, and every bit as accurate as my old Remington bolt action .22. It's fun to shoot, but only functions with Long Rifle ammo. It's also a little complicated to take apart and reassemble for cleaning. It's accounted for it's share of rabbits and squirrels, sometimes at surprising ranges, out around 75-80 yards on jackrabbits.
Personally, I prefer revolvers, but own and shoot both in a variety of calibres. One's not better, just different, than the other.
