Good thread (the topic is a perennial around here), and I think the first few posts nicely covered the strengths of each model.
I have a Buck Mark Plus with a 5.5" barrel and like it a lot. Splendid trigger out of the box, easy to shoot accurately, looks good. I also like the Buck Mark's 1911-style grip compared to more sharply raked grips.
My pistol has lately gotten a bit finicky about chambering the first round; after racking the slide back I sometimes have to give it an extra tap to close it. It then shoots fine. I am not convinced this can't be cleared up with some aggressive cleaning, but thought I'd mention it. I would not be surprised to find that the Ruger .22s have an edge in durability.
I am casually interested in acquiring a second .22, a longer-barreled version for real snotty accuracy, put a red-dot scope on it. I love the looks of the brand new Ruger Mk-IIIs, but like all the new Ruger semi-auto pistols they are flagrantly, annoyingly over-safetied. Bleah. I fear I will have to stick to Ruger's fine revolvers from now on. And I will probably go with a Buck Mark Bullseye or a S&W 41 for my next .22.