Its been said before, but I will reiterate that [for me at least] it comes down to:
a) the ability to fire through clothing, against the body, through a bag, etc. Try doing this with a semi-auto and you are asking for trouble.
b) the revolver generally stands up to dirt and grime better than a semi-auto..not always the case, but certainly worth considering.
c) ease of maintenance- I believe the revolver requires much less than the semi-auto.
d) generally speaking, the revolver is less prone to malfunction vs the semi-auto; with the semi-auto, if the gun does not fail, the mags certainly can.
e) ease of use and readiness- point and shoot [easy to understand "manual of arms"]; also, unless you carry the semi-auto with a round in the chamber (along with no safety engaged), the revolver maintains a higher state of "readiness."
You get the general idea. Now, having said all of this, I still prefer to use a semi-auto. But, this is simply due to the fact that my method of carry allows me to feel comfortable with such a decision. In addition, I do enjoy a slightly higher capacity, even if this only averages out to an extra 2 or 3 rounds (based on my current weapon of choice).
However, the only real negatives I can see with the use of a revolver is lack of capacity, relatively heavy in weight and the idea that when a revolver fails, it is either minor or catastrophic...usually, there seems to be no in-between. These were among my considerations for using a semi-auto. However, for my wife, should she ever carry, I would certainly recommend a revolver nonetheless.