Perhaps even older than the perennial argument about the relative superiority of 9 mm vs .45 ACP is the argument about the viability of the revolver vs the semi-auto as a self-defense weapon.

There are still those that claim that the revolver is a better choice for some classes of people, most notably women. The argument is that a revolver is simpler, and easy to operate. Presumably, the implication here is that women are also simple and mechanically inept. Not only is this untrue (at least in my experience) but it is inviting (at minimum) a poke in the eye with a sharp stick.

So lets take a look at the relative advantages:

• Capacity. The smallest semi auto is competitive in terms of capacity. Small revolvers firing decent power ammunition will typically have 5 or maybe 6 rounds. A small semi-auto will typically hold 10 rounds. Even the minute Ruger LC9 9mm holds 7+1.
• Reloading. Reloading a semi auto typically involves pressing a button to drop the empty magazine, sliding a full magazine into place, then releasing the slide. A revolver typically involves pressing a button to release the cylinder, swinging the cylinder out, hitting the ejector to extract the used cases, then loading rounds, typically one by one into the cylinder and finally closing the cylinder. This can be sped up by the use of speed-loaders, or moon-clips. The only disadvantage to these being their bulk.
• Physical size. One of the problems with a revolver is that there just isn’t much you can do about the diameter of the cylinder. For a given capacity, a semi-auto is always going to be smaller.
• The slide. The slide on a semi-auto is probably the  most intimidating part. Having that chunk of metal whiz back at blinding speed 1/8″ above your hand is disconcerting until you get used to it. Then there is the problem of racking the slide. The spring on some guns making this a challenging task for the uninitiated. However, I contend that with a bit of coaching, I can get people who claim that they just can’t do it, happily racking their slides in a couple of hours. It is mostly technique, although there will undoubtedly be some people with real physical problems for whom this will always be a problem.
• The cylinder gap. The gap between the front of the cylinder and the barrel leads to a blast of hot gas (flame) and potentially small pieces of metal blasting out with each shot. Unless you fire a revolver in the darkness, this is often unnoticed until someone gets a finger or hand in the way. As with the semi-auto slide, dealing with this is simply a matter of training yourself to keep your hands well away.
• Mechanical complexity. The revolver is typically touted as being mechanically simpler. In fact, it is arguably considerably more complex. Leaving aside the trigger/hammer/sear which is reasonably consistent across revolvers and semi-autos, a semi-auto (non 1911) consists of basically a chunk of metal (the slide), the barrel and a spring. You can’t get simpler than that. If you want, you can add in a box and spring for the magazine. A revolver is more complex. As you start pulling the trigger, the cylinder has to un-lock so that it can rotate. The cylinder has to rotate the next cartridge in line with the barrel, accurately, to a precision of a thousandth of an inch or so. The hammer is rising at the same time. Before the hammer falls, the cylinder has to be locked in place, then the hammer falls. There is a lot of precision placement and timing going on during that trigger pull. From the outside a revolver may look simple, but internally it is relatively complex.
• Jamming. Semi-autos seem to find an endless variety of ways in which to jam. In reality, they are all variations on  a couple of themes: extracting and ejecting the empty case and feeding the next round from the top of the magazine. Short of the dreaded double-feed, most jams can be fixed by the slap-rack-bang technique. Revolver jams are usually due to a single cause: There is a lot of leverage cylinder to trigger. Just try holding the cylinder between two fingers and pulling the trigger — you can’t. So the revolver depends ipon a very freely moving cylinder (when unlocked). Small amounts of dirt from just about any source in the wrong place will make the cylinder rotation stiff, and the trigger pull impossible.
• Ammo problems. There are two (rare but important) ammo problems to consider. The first is a squib load – too light a charge of powder. The result is the same for revolver or semi-auto: a bullet lodged in the barrel, and the distinct possibility of losing at least a finger or two if you pull the trigger again. The second is a hang-fire. On the range these are easily and safely dealt with, just keep the gun pointe down range for 30 seconds, and if it doesn’t go bang, it is safe to remove the dud bullet and continue. In a self defense situation you cant do this. With a semi-auto, you just rack the slide – taking care to keep fingers and eyes away from the open action in case it does go off. With a revolver, you really can’t pull the trigger again, because the fizzling round will rotate to a position where the bullet has nowhere to go. If it does fire it will probably take the side out of the cylinder, and maybe half your hand with it. All you can do is a full eject/reload. Rare as hang fires are with modern commercial ammo, they do happen, and this, above all, is probably why I would not use a revolver for personal defense.