I love both types of entertainment at receptions because they each bring something special to the table.
My first encounter with a wedding band was at a lavish wedding near the beach in SoCal. During the cocktail hour, only the pianist, the trumpeter, and the bass guitarist played; a few sets of light jazz was a perfect transition from the beach wedding to the tents set up on the grassy area nearby.
It was terrific to have a graceful live performance accompany the easy, breezy style of the cocktail hour; I think a DJ would have been too overwhelming and possibly stifling in this environment. The jazz trio just seemed to fit so elegantly. They responded quite easily to the swells in conversation, filling up the space with music as conversation weaned and backing off when the guests' voices joined the cacophony. The band leader was an amazing MC; as a consummate professional, he even had written down the phonetic spelling of the wedding party members so no one was mispronounced. After dinner, we all got up to dance to some super funky tunes with a great line up of Motown classics, including Ain't No Mountain High Enough (the link is a sample wedding band; the actual band from this wedding story no longer exists, sadly) and ABC by the Jackson 5. The band only took one break during the three hours of dancing but made sure to have background music on cd to keep us dancing fools going until their return. I imagined that all wedding bands were this amazing and fabulous!
Then several weddings later, I was a groom's attendant (I have a lot of amazing guy friends who want me to support them on their wedding day, so I've been on the groom's side many times) where the wedding band was a little more lackluster. The bride and groom had invited almost only family members and there was a large older population. The wedding band was more of an oldies band playing songs from the 1950's and 60's. While songs from the 1950's are fun to dance to, the band seemed out of sync and sloppy. We winded down the dancing much earlier than the crowd was ready for because the band had a limited repertoire. The bride and groom didn't notice as much as they were busy meeting and greeting, but the reception lacked the spirit I expected from a live band. When I asked the groom about it later, he said they had a limited budget and really wanted live music. I think they should have spent their limited budget on a really good, family-friendly DJ to get the most bang for their buck.
When picking a wedding band, there are tons of online tools that can help: websites, online reviews, and video clips. It's your amazing celebration, so if live music is in the budget, make sure you're vetting out the band thoroughly! Some of the following questions and guidelines should help:
Wedding bands are an amazing addition to the life of a reception if they are good, have great taste in music, and know how to get the crowd going.