Ratchet Guns are less expensive, but are more difficult to use. To stop caulk flow on the ratchet gun, the user must turn the piston so the ratchet disengages.
Smooth Rod Guns are more expensive, but are easier to use. With a smooth rod gun, the user simply disengages a quick-release thumb plate to stop the flow of caulk. Drip-free smooth rod caulking guns allow the piston to back up slightly after each squeeze so the user does not have to turn the piston or depress a lever to stop the flow of caulk.
Some models use an automatic vacuum action to draw any unused caulk back into the nose of the tube.
Power Guns that operate with a rechargeable battery pack are becoming popular with pros and serious d-i-yers.