During my time as a professional wedding photographer I have seen a lot of DJ's. They come in many different sizes and styles. The two things I always tell every couple that I meet and it has always held true. One deligate on your wedding day everyone around you wants to help and make it a great day. The second thing I say is it is your wedding. With that in mind think about what kind of DJ you want.
Think about what kind of music you would like to have at your wedding. There are certine DJ's that specialize in a ceretin kind music. You can get people who specialize in laid back Frank Sinatra or people who have air guitars and play 80's heavy metal. Like I said they come in many different varieties.
There are DJ's that get the crowd going and organize photos. I have recently worked with one of the best last weekend. He helped me organize some great wedding photography group shots and was genuinely wanted the couple to have a great time his name was Tod Peavy.