What is the condition of the particular used guns? If it's as good as any of the rest, I'd get the M66, which I feel is the best all-round sidearm ever made, unless you need to shoot a lot of .357 ammo. Then, I get the M686, but that price is too high.
Smiths have better trigger actions than Rugers and better resale value. They're usually finished better, too, and command more respect among serious handgunners.
Lone Star
P.S. I've owned every gun you mentioned, if that qualifies my commentary.