I'm for different powers for each zombie type. Possibly something that counteracts there weakness's or helps there strength's more. ex

(/=or)
Classic: Takes less damage/more durable
Predator:Goes completely invisible for short duration 2-3 seconds/ Higher jump radius
Speed: Less knock back for a short duration 3-5 seconds/ More hp
Deformed: Speed boost for short duration 2-5 seconds/Burn damage doesn't affect for short duration 5-10 seconds

Tons of other suggestions prob better than these but all i could come up with on the spot. Believe it would help make things unique because there would be diff powers for each class.