I've owned a Security Six, a SP101, and a Blackhawk. Just to judge the gun overall without regard to use, Blackhawk hands down. Now, IMHO, the Security Six finishes way last by a country mile to the other two. The little SP101 is a stronger gun, a more accurate gun (at least mine was, even with a 2" barrel vs 4") and an easier to carry gun to top it off. Funny thing, I found it more comfortable to shoot with hot loads, too, even though I had Hogues on both guns. Now, I've never really cared much for the GP100, but I'm sure it's better than the Security Six even though I've never owned one. I won't rank it here since I've never had much dealings with 'em. It's a heavier and stronger version of the SP101, though.
I did sell, for various reasons, the SP101 and the Security Six. I mean, they were good guns, just for reasons, I decided I didn't need the Security Six and I had told my son-in-law I'll sell him back his SP101. I really didn't need it, but it was a neat gun in a lot of ways. If I got another, it'd definitely be a 3" gun. It is NO pocket revolver IMHO, too heavy and needs the Hogue grip, so the 2" seems goofy to me.
I'd probably have kept the SP101, though, good little gun, had my son-in-law decided he didn't want it back. I woundn't even THINK of selling my Blackhawk, though. Of course, I'm a hunter and outdoorsman. It's no concealed carry gun, though at least one person on this board from the bay area would, no doubt, argue that point.