2" for dedicated CCW, 3" for compromise range gun
If its for pure concealed carry/self defense, get the 2". If its a compromise gun (range/HD use), and will be carried on the belt, get the 3". For defensive purposes the .75" won't make a difference in a bad way but there is a small chance it could be a benefit.
Mechanical accuracy is better than you will be. There is a video of a guy on YouTube hitting a soda bottle at 100 yards with 1-7/8" barrel. Longer sight radius is the real trick. There are other advantages to short barrels like faster time clearing the holster, easier to maneuver in extreme close quarters combat (ECQ), and harder to get it taken away from you.
If you are really serious about this read Ed Lovette's book Snubby Revolver.