I have only done RCCL once. They are not good to solo cruisers.
I was on the Voyager of the Sea. At first glance it looked impressive but I found the promenade to be a little claustrophobic and all bunched together. I think Carnival's ships have their stores, shops and bars more spread out. On RCCL there are cabins overlooking the entire length of the promenade. Therefore you have several floors of walls of curtained windows going straight up. No way to get a sense of space or outside. That made the promenade feel more narrow then it probably was. On Carnival, one would only have to walk a few steps in order to look out of a window. It gives the illusion of openness even if it is not.
Also, a lot of the big bells and whistles on RCCL newer ships are not something that I will participate in: rock wall climbing, water surfing, ice skating, virtual golf, and I don't cruise to do mini golf or go to Johnny Rocket.
Therefore, for the difference in price for this solo cruiser, I like Carnival just fine indeed.
Perhaps if RCCL ever comes up with a reasonable pricing alternative to 200% for a solo cruiser I will give them another shot. However, right now I can't justify paying $1,000-$1500 for what Carnival will give me for $500-$750.
Go with the idea that Carnival did not become the biggest and most popular cruiseline by accident. They know what they are doing, they offer it for a reasonably price and they do it well 99.999999999% of the time.
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)