Who should be in the delivery room?

My hospital only allows two people to be in the delivery room while giving birth.  Of course my husband was in the room with me but the extra person my first son it was my mom. With my second son it was my MIL. Who should we ask to be in there with us for our third child, our first girl? I'm thinking maybe my SIL (if she wants to since she is 18) or maybe just my husband to keep it fair between our moms. What do y'all think?