My thumbnail sketch for a GP 4" Smith revolver with adjustable sights:
Shooting .38s Specials only: A Model 15 or 67. The 15-3 that I have is target-grade accurate.
Shooting .38s, but you want the ability to shoot a magnum load now and then: Models 19 and 66, keeping in mind that high-speed, lightweight .357s are bad for almost all of them. The newest ones with the ball-detent locking system supposedly are good with those rounds. If recoil is an issue, you'll know it with one of the K-frames and .357 rounds.
Shooting .38s and .357s a lot: Models 586 and 686. There is enough meat on those guns to soak up a lot of magnum recoil.
Shooting .357s from can see to can't see: Models 27, 28 and 627.
I've no trigger time behind the lightweight N-frames, so I'll refrain from commenting on them.