Spring Alfonse: +def/-spd or +spd/-atk?

+spd for sure. The +10 damage to special helps a lot with that -atk. The only situation where I could understand choosing the -spd one would be if you were running a defensive build that tries to get doubled on purpose to charge his special faster, which I assume is not the case(and even then, there are other units for those builds, while Alfonse can capitalize on the speed boon better than them).