we have been on both. Royal first recommended bt TA. We have two chidren and she thought Royal would be better. Next cruise was Celebrity and we would never go back. We Did try HAL once-nice but still not Celebrity. Main reason is suite service. you do not get it on any other line.
As I mentioned we travel with 2 teens now and they love it. There are kids but on Celebrity but not hundreds. We are booked aagain on Mercury 3/06--can't wait