I have both a Ruger 22/45 (Black/Blue) with Bull Barrel and a Buckmark, but the Target model in nickleplate.
Ruger 22/45, There is this kind of target shooting competition called Bullseye shooting, where you are suppose to use a 45 Auto, a "center fire" (most use a 45 auto), and a 22 rimfire in the competition. My understanding is that the Ruger 22/45 was created so that NRA Bullseye shooters would have a 22 that had the same angle of the grip compared to the barrel as with a 45 ACP M1911 A1. Also the layout (i.e. where it is on the pistol) of the safety and magazine release on the 22/45 was to allow a Bullseye shooter to not get confused when they changed handguns.
The other real plus for the Ruger 22/45 is that as a gun designed for use in competitive shooting, there are lots of aftermarket assessories. There are plenty of websites where you can go and buy scope mounts, special trigger assemblies, and get all kinds of special trick gunsmithing done for your 22/45.
The Rugger 22/45 like the Mark II has a tricky disassembly method, but once you figure it out it isn't that bad. There are websites that will explain the trick for you. (Make sure you find one and study it BEFORE you take your Ruger apart!). There are also after-market kits that will modify your Ruger so that the problem goes away and the disassembly is more traditional.
I am not thrilled by all the plastic that the Ruger 22/45 incorporated into its design. However, it is solidly built and I have had no problems with the plastic cracking or melting with cleaner solvents.
The Buckmark, as said above and in mine, has a sweet smooth trigger right out of the box. One problem with a Buckmark if you have kids or a typical wife, is that it requires a bit more hand strength to operate the slide to chamber a round, then the Ruger. That is the Ruger T-shaped end cap is very easy to grip and cycle a round into the chamber. The Buckmark ridged slide can be a bit hard to grip tight enough to cycle. Since there are far less Buckmarks out in the world, the amount of aftermarket stuff for them is much more limited.
I enjoy shooting both without any extra features. They are both accurate. They are both reliable. I shoot my Buckmark more often than I shoot my Ruger 22/45. My two sons enjoyed the Ruger much more.
I hope this helps.
