Honestly, all of them.
I suppose I should have the god-given shame needed to regret selling the Colt Viper... but I don't. Same for the 1970s Python, The Delta (a 'milspec' Colt 1991 in 10mm they made like 500 of) and the M45A1. On the S&W front the Frank Glenn 627, the 25-5, the 629 Mountain Gun, the 3" 65... all of them really do it for some people but just weren't for me. If the 25-5 had a 4" barrel instead of 6.5" I'd probably still have it. Probably. Maybe.