For machining dovetails, there’s really only one choice, but it’s a perfect one. Dovetail bits make dead-on angled slots in a single pass, and they can be used with a number of jigs and templates. (For template use and for many commercial jigs, you’ll want a dovetail bit with a shank-mounted guide bearing.) These bits excel at making traditional dovetails, of course, but used in a router table with a fence, they’re also your best choice to create sliding dovetails useful for carcass joinery. These sliding dovetail joints are like dadoes on steroids: They have the strength of a regular dado, plus the locking power of a dovetail. Unlike traditional jig-made dovetail joints that are made with a combination of dovetail and straight bits, sliding dovetails use the same bit for both the angled groove and the tongue — a single pass is all you need for the groove; one pass on each side makes the tongue.
Dovetail bits are available in a variety of angles, from 7 to 18 degrees, with 14 degrees being the most commonly used. For sizing your dovetails, you’ll find bits in a range from about 1/4" to 1" in diameter.
All router bits should be kept sharp, but this is especially the case for dovetail bits — a dull bit makes for truly ugly dovetails with lots of “furry” tearout.