The best cabins in the fleet are usually agreed to be the suites that are aft wraps, which Id get if you can.
As far as all the sweeping generalizations about Carnival's cabins all being larger than RCL's its pretty much just that .. a generalization. For instance the overall s.f. of the newer RCLs ships balconys is actually larger than a standard balcony on Carnival. Carnival cheerleaders will say but the inside part of the cabin is larger, true. you get a 185 s.f. cabin with a 35 s.f. cabin standard, but the inside part of the cabin is only a few s.f. larger, and the balconys are generally smaller.
I would go someplace like cruisedeckplans.com and look at the actual s.f. of the category you are wanting to book, and then looking at a RCL ship you know and actually comparing the s.f. .. if its important to you.
As far as I know only Spirit class has suites that are aft wraps. The aft wraps on conquest class are superior balconys, 9s, but smaller than the suites on spirit class.