For a revolver that is meant to cover a variety of uses, including carry for personal defense, target shooting, sitting on the hip while fishing & hiking, etc., I am a big fan of a 3" barrel. It is easier to conceal and carry than a 4" barrel, and MUCH easier to shoot well than a 2 1/2" or shorter barrel, as well as providing more power from your chosen round than the shorter barrels. I think the 3" barrel length is an excellent compromise in a "jack of all trades" gun.
As for caliber, I prefer a revolver chambered for .357 Magnum, though I usually carry .38 Special +Ps, and most of my target shooting is with .38 Specials or a light .357 Magnum load. It's nice to have the option to use the more powerful ammo when I want, or the more easily controlled +P .38s or light target .38s for most social work and target shooting.
I'm not gonna get into brand, so much. Ruger and Smith & Wesson make excellent .357s in various sizes and flavors. There are other brands, some of the quite good, but these are honestly the only two current revolver manufacturers I'd buy from.
BTW, my current carry gun and all time favorite handgun is my Ruger SP101 .357 Magnum, with a (you guessed it!) 3" barrel A review I wrote about mine can be found here:
Ruger SP101 w/ 3 1/6" Barrel Review