It really depends on what you want out of the pet. For PvE it is all about the specific encounter and the pet's moveset. Sometimes speed is better, sometimes power is better.
For PvP you don't know what the encounter is going to be like, so it goes to the moveset only. The sporeling sprout has crouch, which benefits from a speed breed, so going s/s means you'll most often go first and get an extra round of crouch. If a pet has moves like stun, crouch, sleep, interrupts, flank/tongue lash, alpha strike, etc., then speedier is usually better (but again, for PvE the actual encounter matters. If your opponent is 205 speed, most any breed will be faster).
For pets like this with multiple breeds and a varied moveset, I find having multiple breeds on hand for PvE is optimal.
Carry Pet Experience Reference Guide: