Semi-automatic pistols vs. revolvers

Both revolvers and semi-automatic pistols have prominent places in the world of handgun applications today. For over a century, however, a debate has continued as to which one is better for which particular application and why. Each has its place, although personal preference is as large a factor as the following variables:

Reliability (likelihood of malfunctions; how to recover from malfunctions; how to recover from misfires)
Degree of user training needed
Degree and frequency of gun cleaning needed
Ammunition capacity
Speed and ease of reloading
Bulkiness with regard to concealment
Weight
Center of gravity
Storage issues
[edit] Advantages of revolvers
Ease of use: Most revolvers have no external safety devices which need to be deactivated before firing nor do they require manual cocking, making revolvers quicker and simpler to put into action. All semi-automatics require manually cocking the slide before firing, and many also have manual safeties which must be disengaged before firing.
Reliability: Revolvers are mechanically simpler than semi-automatics so are less likely to suffer stoppages or malfunctions.
Fault tolerant: In a double action revolver, if a round does not fire, a pull of the trigger will move a new round into firing position and fire it. In the case of single action semi-automatics, the hammer, if one is present, must be re-cocked in order to re-strike a dud round or the slide racked to remove it. Some double action semi-automatics can re-strike a dud round by pulling the trigger again, but as with all semi-automatics, the slide must still be racked to clear a round that will not fire.
Potential for greater stopping power: The largest and most powerful handgun cartridges are designed for revolvers, owing to their more robust design.
Revolvers will easily fire blank ammunition. Most semi-automatics will not fully cycle with blank cartridges, causing malfunctions. Semi-automatics must be specially modified to properly cycle with blank ammunition. This modification renders them incapable of firing other types of ammunition.
Spent cartridges are kept in the cylinder making them easier to retrieve for hand reloading or clean-up. Semi-automatics eject cartridges some distance, requiring them to be retrieved for hand loading or clean-up.
Greater variety of ammunition: Revolvers can handle a wider variety of bullets, including wadcutters, which will malfunction in most semi-automatics. Wadcutters are designed for target practice, making revolvers more appealing to many sporting shooters.
Multiple calibers: Many revolvers can load certain interchangeable cartridges, those with identical bore diameters but different case lengths. Interchangeable cartridges include .22 short/long/long rifle and CB caps, .357 magnum/.38 special, .44 magnum/.44 special, and .45 Colt/.410 shotshells. Note: Please check with the manufacturer.
Greater accuracy: Sights are mounted to a fixed barrel, theoretically allowing greater accuracy.
Easier to determine if loaded: In most revolvers, the cartidges are readily apparent when loaded. An unloaded semi-automatic is often visually identical to a loaded one.
Easier to clean and maintain: Revolvers have few exposed moving pieces and do not require disassembly. There is no risk of loss or breakage of pieces when cleaning a revolver. Semi-automatics must be disassembled for cleaning, which may be difficult and risks losing or breaking vital pieces in the field or in darkness.
Advantages of semi-automatics

Smith & Wesson 9mm semi-automatic.Larger ammunition capacity: semi-automatics typically carry around 7 to 20 rounds; whilst most revolvers carry between 5 and 8 rounds. Magazines are limited to 10 round capacity in some jurisdictions, such as California, largely negating this advantage in those jurisdictions.
Compact ammo storage: The flat shape of most magazines make them more convenient to carry than the speedloaders needed for revolvers.
Slimmer profile: Semi-automatics often have a significantly slimmer and easier to conceal frame as they do not suffer from the bulge produced by cylinder of a revolver.
Lighter: Some modern semi-automatics have frames made of polymers, making them lighter and more comfortable to carry for long periods. Recent advancements in technology and design major manufacturers are producing polymer frame revolvers like the Ruger LCR, Smith & Wesson Bodyguard 38, and Taurus Protector Polymer that rivals the weight of polymer semi-automatics.
Safety: Some semi-automatics incorporate an external safety switch, which prevents the gun from firing. Most revolvers do not have such a feature, though the same is true of many semi-automatics. There is debate over whether external safety switches are necessary, particularly in models with trigger-activated firing pin blocks, though many users prefer them for peace of mind regardless of whether or not they are safer.
Quieter: With similar ammunition, a semi-automatic is typically slightly quieter. Flash and noise can be suppressed. Noise and flash suppressors are ineffective in most revolvers due to noise and flash escaping the gap between the cylinder and the barrel. Suppressors are illegal in many jurisdictions.
Less expensive ammunition: semi-automatics often fire standard military ammunition, which is more readily available and cheaper thanks to extensive mass production. However, some revolver cartridges such as .38 Special are comparable in their cost and availability to popular autoloading cartridges such as 9mm Parabellum and .45 ACP