Agreed, with one minor difference than SM: I'd rather buy full spares and trim yourself to St. Louis. Less expensive that way, and there's some really good meat (hello, rib tips) above the joints and below the chine. Don't buy any "manager's special" that has already been spiced--that goes for anything, including ribs. Unless you're buying known fresh, make sure it's in the original Cryovac packaging. Age old food service trick to pull what hasn't moved by expiration, slather it in something, and repackage with a new expiration date on it. Single service C-Vac's allow you to inspect the product from all sides, unlike the styro trays and multiple items sandwiched together.
That said, you need to try them all in order to formulate your own opinion. Beef ribs, baby backs, spares, lamb--even cabrito--have their own nuances that make them each special: try all of them like Red suggested. Experiment with the different woods: and regardless what's said, you still have to try mesquite to find out whether or not you like it. Words of caution are that it burns hotter than other woods and is stronger, so you don't have to use very much. Don't limit yourself without trying them all and relying solely on others' opinions. Good luck!