we've done 4
DCL, 3 RCCL, with 1 more DCL booked and 2 more RCCL booked (so by spring break 2008, 5 of each).
Enjoy both, each has their place. DS, 10, ranks a Radiance class ship and DCL as equally desireable. We'll see how much more (we think) he'll like Adventure of the Seas, Voyager class. Won't do Freedom class for so long as they are exclusively Miami-based--really don't care for Miami as an airport, seaport, or in general as a place to visit.
Disney has a feel that can't be duplicated, but RCCL offers more variety for itinearies, and frankly, sometimes the difference in price just gets too much to ignore (I agree with the general principle that you get what you pay for. For Xmas 2007, the price of our Magic cruise in a cat. 8 would get us a balcony, D1 stateroom on the Mariner, so I get the Disney intangibles--and tangibles--at the expense of "losing" the balcony. I can deal. For thanksgiving 2006, however, the D1 balcony for 6 nights on the Radiance is $2209, vs. $6,068 for a cat. 6, which is a fair comparison (really a cat. 5 should be the fair comparison, but we'll leave it at 6) so far as stateroom goes. Even accounting for 6 days vs. 7, it is a no-brainer (also don't mind having the sunday-saturday itinerary, leaves more travel time at either end, along with more prep and recovery time as well).
If prices were always equal, I'd still make some RCCL ressies to get the itinerary variety--such as being able to do 4 nights in the caribbean rather than the bahamas, in our case on the Enchantment, this past Feb. (a stateroom darn close in size to a cat. 8 for 4 nights for $529/pp!!--couldn't come close to touching that on DCL for their 4 niters, and prefer the better likelihood of warmer weather in Feb. rather than the hit or miss weather in Feb. in Bahamas. Or back in January, got 6 nights in a suite for Western for the same price as 7 nights in a DCL oceanview. A no-brainer, even though we missed the production shows. Though if prices WERE equal, there'd be other times I might opt for DCL, instead of RCCL.