I'd choose the back based on knot placement, reflex or deflex of the stave, twist, etc. Since it seems like you have a log that's curved, I'd split it so one half is reflex and the other half deflex, so you don't have to do any heat correcting later, and you can always recurve the tips on the deflexed stave. That depends how big the log is though, what's the diameter on yours?