Of the handguns I have I find I end up using on of three, which allows me to shoot most competitions.
1. Glock 17 (9mm standard model)
2. Smith & Wesson Model 14 (38 Special, 6", Millet sights)
3. Smith & Wesson Model 65 (357 Magnum, 4", Fixed sights)
This combination allows me to shoot a fairly large number of events, reasonably well. In addition they are quite cheap to buy and to run.
The two revolvers are K frames which allows sharing of a certain amount of equipment between them.
Scooter2 is correct though if I were to choose a single gun I would consider a 1911 style double stack gun, in .40S&W