I agree with BrooklynQ. Go with what you do best. We do babyback's better and if we're going to practice ribs, I want to enjoy it the best if I'm spending money on the meat.
All I read about is how spares are tastier, moister and more forgiving etc.. That may be true.
However in my cooking experience the loin backs always seem to come out better, have more flavor, don't fall off the bone excessively etc. I definitely feel more in control of the baby backs. My butchering skills trying to trim spares into St. Louis style also still need work which makes it easier for me to go with babys at this point.