I would agree with your ranking. While my own preference is for Toks without added safety,IMHO in order of collector value I would rank them "a", then "c", then "b". The first one, as farmall suggests, is "Not messed with by importers or private owners. Just mixmastered during service." The third one is also nice because it lacks the import mark and added safety and, as unfortunate as it is, it was not uncommon to have these "trophy" pistols nickeled or chromed. In essence, this refinishing by the soldier/owner becomes part of the pistols history. The middle one, again IMHO, is just something "butchered" by the addition of the import marks (if billboard-style) and especially the safety. Personally, I would choose not to own a TT-33 before I ever picked up one with the added safety.
Just my .02 cents.
I would prefer one with safety to no Tokarev of that particular type.