Whats the differetnce iN the mk line Up a buddy bought one for $375 used believe mkII
Mark II is an older model while Mark III is the current production model, as is the 22/45 series. The biggest difference between the II and III versions is the II has a mag release at the bottom of the mag well, and the III has a thumb button like most handguns today. One other notable difference is the MK III has a magazine safety mechanism (although it can be removed) while the MK II does not.
The 22/45 is basically the Ruger MK III but with a polymer frame and different grip angle. (It also takes different magazines, or at least different magazine floorplates)
There are two main versions of the 22/45, one with removable grip panels and one without. I would recommend the one with removable grip panels, if you decide you want a 22/45 as this will allow you to get different grips for it.
And of course there are various barrel lengths available for each.
Personally, I would recommend a Ruger Mk III (or 22/45 if you actually like the grip angle better) over the S&W 22a. I think the rugers have a lot more parts/upgrades readily available for them (such as: grips, trigger kits) than the 22A. Neither the Rugers or the 22a have a particularly great stock trigger, so you will likely want to upgrade it if you want to shoot bullseye.
I'm definitely biased though, since I've been using a MK III and have been pretty happy with it.