The absolute most fun I have ever had shooting a handgun was a "Schnellfeuer" Mauser 96. I don't own it and only got to fire it one afternoon, but it was a LOT of fun.
The one I seem to enjoy most of mine is a S&W 17 6". I can blow through a couple bricks of .22s without breaking the bank, a wrist or an eardrum and it's accuracy is right up there with anything else I own.