So far I feel RCCL has the best room service. They have a complete menue and anything served in the diningroom can be ordered through room service. If you do not see it on the menu just ask. The kids will call down for room service in the evening. They tell them they want snacks. They have been sent a dozen cookies or brownies and big glasses of milk. They have great turkey sandwiches which is great after a long day in port before dinner. They offer a full breakfast menu which Carnival and NCL do not. We have always found the service to be prompt. Usually less than 30 minutes. Our waiter who brings it has always been friendly and smiling. Always offers to set it up for us on the balcony or serve us breakfast in bed!
We always tip a few $$$s. For this reason we bring along lots of dollar bills.