I have used both of these Pokemon for several different roles before. I will give you an overview of both.
Pros: Good Attack, high Speed, great Ability, wide movepool, and quite diverse.
Cons: Low defenses so he can be OHKOed by any strong Neutral attack.
Good Ambipom sets
Pros: Good Special defense, High speed, and a nice movepool
Cons: While it has ok defenses a strong fighting move will OHKO it, and it has low defenses so it needs to use Work-up in order to be offensive.
Good Lopunny sets
I would choose Ambipom, he is faster and has good offenses and plenty of uses.