Well it depends on what you want it for. If you want to shoot targets or hunt with it, a longer barrelled heavy gun like the Model 27 would be better. Heavy guns absorb recoil better and are more fun to shoot. If you plan to carry it for self protection, a lighter gun with a 4 inch barrel would be better. The heavier the gun, the harder it is to carry; even with a good holster. However, lightweight guns are less pleasent to shoot because of increased recoil.
I found out that there are some guns designed to shoot alot but carry a little, while others are designed to carry alot but shoot a little.
The model 686 is a popular model available with long barrels for accuracy shooting or short barrels for concealment. The 4" version would be a decent carry gun. For lighter weight, consider the model 620.