I'm sailing on the Valor in July - this will be my first Conquest Class Ship. I've never been on a Celebrity Cruise, but a lot of the older folks I know love Celebrity.
Carnival is not Celebrity or RC. It is a budget friendly line that's great for folks entering the cruise vacation space at a cost that works for them. Personally, I love Carnival - but I love it because it's always fun, the CDs and ship events are hilarious, and my kids love it. (I have well behaved kids who know better than to cut a fool.) Oh - and I love the soft serve ice cream machine. LOL
I sailed RC Majesty of the Seas once and hated it. Ship activities were ok, but didn't like the ship - it was dated, the pool was out of order a lot. We had fun, but my friends and I decided if we ever did another RC ship - it had to be newer.
All of that said - your vacation is what you make of it. I've meet some great folks on my Carnival trips - and still keep in touch with them! I wouldn't worry too much about the crowd - go do what you like - Bingo, casino, karaoke, etc, and have a good time!