I've owned a Glock 34, twice. Bought it the first time, thought it was great (and it was), but I shot my Glock 19 as good or better, so I sold the 34.
A couple years later, a good deal on a 34 came up, so I got it, shot it, and still shoot the G19 better... so I sold the 34 again.
I shoot the G19 Frame also better than longer ones. I also shoot my G32 more accurate than G19 or G23. I did pick up a XDM 4.5 in a 40 cal, this gun is also a good shooter, I seem to hit better with it than my other longer 40's. My sights have all been replaced with TFO and that helps me much better than plan sights. If it may some day save ones life do what you must to be CONSISTANT with your carry weapon.
I think it will depend alot on the shooter and the distance personally I have a 2 xd 40's 1 subcompact and 1 4" service model and my carry preference is the sc bc of the smaller size and its accurate enough to get the job done but my 4" is far more accurate that the sc with 3'' barrel