The food on Celebrity is much better. I had a waiter on RCCL advise me not to get the lamb because is wasn't very good. He was right. I have had it on Celebrity & it was delicious. I have never had a waiter on Celebrity suggest that something wasn't very good and to try something else.
The showers on RCCL are tiny and in a corner! Celebrity's are more like a shower stall at home. If you are taller than 5'8" and heavier than 100 lbs, be wary of those showers.