Depends on the sanctioning body. You and I are largely in a similar region. MBN definitely go with baby backs, cut 2 bones per piece. KCBS definitely go with St Louis spares, cut 1 bone per piece. They define what is the perfect rib differently.
GBA, baby backs, as it came largely from MBN guys. FBA, probably St Louis, dont know...
Unsanctioned; your guess is as good as anyones. I'd probably cook baby backs and have this overcooked to the point of falling off the bone tender.
Why? Because the sanctioning bodies define that perfect rib differently, and along the way the judges at the sanctioning bodies have become accustomed to a particular style of rib. Surprises often times are punished.