Erreertt,
I have a MKI, MKII, and a MKIII 22/45 and I like them all. IMHO I think the MKII is the best of the series. It has the last shot bolt hold open that's lacking on the MKI and none of the lawyer crap the MKIII has (mag safety and LCI, lock)
That being said the mag safety and LCI are easily removed from the MKII. But I'm going to stick with the MKII being the best. I think Ruger put a bit more care into their guns back then.
What ever model you get, get a McFadden loader, well worth the money!