A couple of pocket holster features that I find useful:
a) Holster cut-away under the pistol grip.
Pro: This allows for fast acquisition of the grip when the gun is in your pocket. This an important feature for me.
Con: It can allow the outline of your gun to be seen through your pants. You may want to put something else in your pocket to break up the outline. A piece of cardboard which is cut to size can work. (Tape the edges of the cardboard.)
Holster pictures with this feature: Hedley, Desantis
b) Thumb-Push to quickly break the gun free from the holster.
Pro: Faster. No fumbling to get it free. Can use tight enough holster to retain the gun in the cut-away holster, and still get the gun free quickly.
Con: None.
Holster pictures with this feature. Hedley.
c) Holster pictures with both features: Hedley.
Those are make or break features for me. Of the four holster pictures posted so far, Hedley would be my choice.