Revolvers work everytime---semiautos do not.
I've had some interesting failures with both in my short time. Might be a little off-topic, but I'll list it anyhow as it might be useful/interesting to people reading along.
- Semiauto pistol failure. I have an annoying tendency to absorb the recoil myself (not sure why I do that, but it's a natural reaction I have that's hard to overcome), rather than letting the gun do the work, which results in an immediate feed failure... Also had some feed failures when the gun was really dry (when I first got it, used).
- Revolver failure. With a brand new revolver, it was failing to fire every second or third shot until I got a box of ammo through it. The hammer would drop, but it would kind of snag/slowdown halfway and not hit with enough force.
- Semi-auto carbine (AR-15). A malfunction while feeding from the right stack of one particular magazine due to the lip being just slightly out of spec.
Personally, I like to have a revolver and SA on me... The revolver has an intricate mechanism, but seems to be more tolerant of dirty conditions. However, it really doesn't have the capacity I like (mine's a 5-shooter). I guess that may take 5 shots to incapacitate an individual attacker. SA gives a better capacity (15 for me, wish it was more, but it's probably enough), but is more fiddly when dirty. I like the AR-15 the best, but people freak out if you walk around with one of those, and I don't think they qualify for CCW around here...