For my 686+ 6" I got an AE Nelson strong side/crossdraw w/ thumb break. It's not much of a concealment holster, even for a 4".
I also have an X15 Bianchi vertical shoulder holster for grins and giggles if I should ever want to conceal it under the trench coat I don't have yet...

4" Revolvers are pretty long, high riding holsters are a challenge to draw from. And especially make sure you've got your reholstering planed out so that you don't point the muzzle towards you as you are trying to reholster. Pancakes are going to conceal amongst the best, but can be a challenge for some people... I would want one that has the cylinder close to belt level and maybe the front cut away a bit so to ease the draw. Lots of makers out there, lots of suggestions here already.
I like TT holsters real well...

Good luck!