Without a doubt, the 357 Magnum.
Averaged from ammunition fired in 5 different snubbies (2 Model 640s, one Model 60 and one Model 340) the Remington 125 SJHP moves out a 1180 FPS. These same Remington 125 SJHPs leave the 3" Model 60 Small Hunter at 1322 FPS and the 5" Model 627s at an average of 1450 FPS. They fly out of the 18" Model 92 lever-action at 2050 FPS.

The Winchester 125 JHPs move out of the same 5 snub nosed firearms at an average of 1205 FPS, 1496 FPS from the 5" Model 627s and 2100 FPS from the 18" Model 92 lever-action

While I have access to 5 Model 940s, I have never chronographed them (perhaps next month). However, the Remington 124 Golden Sabers claim roughly the same velocity from a full size auto-loader, not a snub nosed revolver.