With the Government model you are just paying extra to have Ruger sight it in and test fire it. It's just a waist of money.
the Government Competition and the Slabside are the same gun. This gun is a version of the Government model that has been souped up a little, and has not been fired by Ruger. That's why the two guns cost about the same. You definitely get a lot more for your money with the Competition model.
That said, I think the KMK-512 (5 1/2" bull barrel stainless) is the best blend of features. Although technically not as accurate as the Competition, the gun still shoots more accurately than 99.999% of all shooters out there. You really have to be in the Master/High Master class before this gun becomes a hinderance. Quite frankly, the trigger of either gun will be a hinderance before then.
The bottom line is that you simply cannot go wrong buying a KMK-512.