Band or DJ?
In my years as a DJ, I have had the opportunity to work alongside several great bands with very favorable results. If you hire true professionals, bands and DJ's will share a stage and, if need be, even share PA equipment.
The advantages of hiring a DJ in addition to a band are, that you still have professional entertainment during the band's breaks, you also enjoy the versatility of the DJ being able to supply virtually any song ever recorded. Professional DJ's also tend to act as coordinator and keeper of the time line in addition to entertainment duties.
The advantages of hiring a band in addition to a DJ are, bands can take a song recorded by Glenn Miller in 1939 and play a superior dance version than Glenn was able to record with the equipment of his day. Also, some bands have specialties, for example, I recently worked with a wonderful Beach Music band and they provided a rousing rendition of "Build me up Buttercup" and I followed it with Madonna's "Music". I couldn't play an oldie like Build me up Buttercup, on CD, with the feeling and style that this band played it and that particular band couldn't play the Madonna song at all. So, as a team, we had the best of both worlds.
I would not make this suggestion for every wedding. Sometimes square footage and budget will not allow for this. Weddings that have either a band or a DJ are not necessarily missing the boat. At ninety nine percent of the weddings where I perform, there is no band. But, if you want to add something special, sometimes a professional DJ and a great band can work together to give you the party of a lifetime!
Ted Crowder Atlanta DJ