I think there was another topic on this exact thing..but not sure. Anyways, I've been on many Carnival cruises. We were on Disney a few yrs ago and saw the Mariner docked there. It was so beautiful, we looked into going on it for a change. Just to see how it compared to Carnival.
I liked things about both. I like the entertainment much better on Carnival...hands down. I also liked the food court much better on Carnival. Much more open and not just the one line which is more like a buffet line on Royal. Now I've only been on the Mariner, so not sure if this is the way they have it on all. But there's many different sections on Carnival to eat and they seem to be open longer than Royal. Pizzaria on Carnival is great...24/7.
The cabins were pretty comparable. I liked the sofas on Royal better. The adult only section pool area on Royal was great. Very nice and quiet.
I guess too you have to look at which ships you might be thinking about. You can't compare one's line older ship to anothers newer.
I did see an older crown on Royal and a little more "stuffy", especially at dinnertime.
We enjoyed having the golfing/rock climbing/ice rink on the Mariner. We did enjoy it and going back next yr. with our kids. Royal doesn't have the slides like Carnival. THis might not be a big deal though. Kids enjoy them..I do too!
I personally thinks it's a good idea to try another line to see what YOU like. It's very subjective. What I might like on Carnival, another may hate. I say try it. The Voyager class has a great teen club. Not sure if you have kids...they have Johnny' Rockets which is a fun place to go.
Well, like I said, I like stuff about each one.
Any specific questions, feel free to email me.