I think the 4" is the best overall barrel length (have 2 S&W 4"). Even a 4" is no target gun though... for that you need a 6".
I don't think there is any "right" answer to this. Bottom line is, you need to be happy with your purchase, and difference people place different weights on various capabilities. No denying the 2" carries better than the 4", but no denying the 4" shoots better than the 2".
I don't currently carry ccw, but if I was concerned much about concealment and carry comfort, I'd actually get a slim semiauto, like a Glock 9mm. Likewise, some people there think a full size 1911 is fine for carry, others think a Glock compact is still too big... personal taste! ;-)