For "friends and family" barbeque I usually buy whichever is on sale. Stores in my area tend to have BB's on sale more often than spares. I can't discern much difference in the texture of the meat. BB racks tend to be a little more even in size from one end to the other. My guests could care less about the "breed" -- they just want RIBS!!!
In competition we use ultra-trimmed St. Louis spares for appearance reasons, mostly. Easy to make them very uniform. A few BB's show up, but not many.
For non-competition spares I like to leave the flap meat on to get a really meaty rib. They aren't pretty but the extra meat is great.
Try this if you can: Whether BB or Spare, the ribs at most grocery stores are sealed in cryovac with some salt water, etc. for preservative reasons (longer shelf life). Find a store or butcher shop that sells fresh, non-preservative ribs of either type and note the flavor and texture difference. I think it is pretty dramatic and I greatly prefer the fresh rib "porkiness" to the preservative rib "hammy" flavor and texture. Fresh ribs are almost never on sale, however
Hub