We have always loved Royal and Celebrity. Celebrity has been our only choice since we have gotten older. A friend and TA recommended to never do Carnival and we haven't. She said it's no comparison. So from reading your post I would recommend you try Celebrity but don't do a ship that hasn't been redone within the past 6 years. The newer or redone ships are in better shape. Just my opinion.
Good review, glad it was a good cruise. We sail Beyond in November and we are hoping I can write a positive review when we return. We usually do the evening dining rooms, so we are anxious about food quality.
You will have no problem, just let your dining staff know. In the buffet you can ask where the gluten free items are. My daughter has Celiac and has to eat gluten free, she has never had an issue.
We have done both and liked them both. I suggest you look at the menus for each and decide on that. If I had to choose one over the other I would pick Luminae. We do love the sky suites also!