Scarlett Jean is a very beautiful name! I love both Felix and Leo so it's hard to decide. I think I'd go with Felix. I just love the meaning of it. I'd probably prefer Leo if it was short for Leonard (we pr. it LAY-o-nard here) or Leopold but I think it's too nicknameish on its own even though I like it. I think they both go well with Scarlett Jean. So yeah I'd say Felix John.