This is really a matter of personal taste. For example:
1. I like a local vendor: http://www.badazzbbq.com/
2. My daughter favors this vendor: Texas Pit Barbecue
3. My son-in-law's favorite is: Armadillo's
4. My brother likes: http://www.carolinaribking.com/
The rib vendors have told me that because it is a contest, they all must use the same style of ribs from the same meat supplier. The difference is in the cooking process and, of course, the dry rubs/wet sauces that each vendor stakes their reputations on.
Some of my friends have a strategy where they buy whole racks of ribs from several vendors and then trade a few bones with one another. This gives them the opportunity to sample a wide variety.
I also recommend that you bring a roll of paper towels or plenty of napkins and also some saniwipes to clean the grease/sauce from your fingers afterwards.