Should I submit more to big agents or smaller agents? Which is more beneficial to me?

Depends on where you are in your career. I know new actors who submit to the biggest agents/managers in the field, because they are fearless and that is what they want. I've seen them have success from that. However, some actors are concerned they will get lost among so many seasoned actors so they go after a strong boutique agent/manager, which is fine. I feel the best agent/manager for you is the one who will get you out there whether they are new and hungry, a boutique agency/management firm or one of the biggest agencies or management firms in the business