I agree w/everyone's posts. We use both lines among a few more. Don't do RCL when kids are out of school unless it is a long cruise or if we are taking G'kids, then won't consider Celebrity.
There is an advantage of Cel. over RC when it comes to Crown & Anchor & Captains Club. Both will recognize the higher category from the other line on their ships (also Azamara) but it is easier to get to a higher category w/Celebrity's Captains Club than RCL's Crown & Anchor.
O F C'er