I used to think a MK II and I will tell you why I changed to single six. I take the Single six to the range as a "back-up" so I don't waste the trip if something goes wrong with what I intend to shoot. Such as the scope was so far off I need to remount it b/c it is outside the adjustable area.
I end up shooting it at least a little no matter what.
The guns I take the most are my Marlin 22 bolt gun and my Glock. If I shoot the glock for an hour I do not want to then shoot a MK II semi-auto 22. A single action 22 always seems like enough of a different flavor that it is a fun way to wrap up a range trip.