White-Winged Dove

Despite what the bird books may say, these doves are bigger than Mourning Doves. I don't know if there is a great debate about such things, but I've seen some bird books place the Mourning Dove at 12 inches and the White-Winged Dove at 11. I think both numbers are a bit generous, and White-Winged Doves certainly appear bulkier, and also usually win out when wrestling for the best spot on the feeder.

They much prefer the arid regions of the U.S. and Mexico, however, and seldom venture beyond Texas, Arizona, New Mexico, and Southern California/Nevada. They're common enough on telephone wires in Arizona, but only during the hot months of spring and summer.
Their tails are rounded on the end, unlike the Mourning Dove's, and they shows their namesake white wing-bars when in flight, and along their flank when their wings are folded.

Mourning Dove

 One of the most common doves in North America, and also the most commonly hunted, the Mourning Dove is still an interesting specimen in its own right. Apart from its tell-tale, gloomy song, the Mourning Dove is the fastest flying dove, and also has a uniquely long tail that fans out to help it break and stabilize when landing.
They can be found all over the continental U.S. nearly year round. Their blue eye-ring and black spotting on their backs help to tell them apart from their larger cousins, the White-Winged Dove.