What is your best company you used for running a promotion/competition on Facebook?
Before you run any competitions or promotions on facebook, you may want to look at this. I found it useful: http://www.socialmediaexaminer.com/facebook-promotions-what-you-need-to-know/
The most common vendors I’ve worked with for clients are WildFire, Buddy Media and Involver. These three tend to get most of the bigger business as well as service some of SMB market but there’s a lot of new players making bold moves especially around the self service model.