I have found that the wikipedia pages for each ship (I just google the shp name and go to wiki) give good info on sizes of ships. Then I can compare them. Is Serenade a Radiance class or Vision class ship? (I don't feel like looking it up right now, sorry.) We liked both Radiance and Vision, FWIW.
We love Royal.
There's a whole forum for them here:
http://disboards.com/forums/royal-caribbean.193/
And cruisecritic.com has a thriving (if snarky) message board forum for Royal as well.
The only thing you'll pay extra for on Royal that you don't pay on Disney is soda.
But if you're wine drinkers and like to bring your own wine, while you're limited to bringing on two bottles per stateroom on Royal (vs 2 per person at each port on Disney), there is NO corkage fee if you wish to bring that bottle to dinner with you.
DCL has a corkage fee if you bring it with you.
Everything else (spa, espresso, special dining venues) is the same. Royal does have some extras on their normal menus; if you want those, the price is *right there*.
Oh, well, if you order midnight room service on Royal you'll pay a small fee. Are there many who order things in the wee hours? I don't.
We have found that the service is better on Royal (and that includes our concierge level cruises on Dream). Food is better in our opinions (vegetarians) on Royal. I like the aesthetics of Royal's ships and their nice white lines vs the heavy ornateness of Disney's ships. and so on.
Royal is definitely worth a try, IMO. We love it.
The onnnnnly issue with Royal is that they have casinos where smoking is allowed. On Freedom that meant we couldn't enjoy the Schooner Bar and their trivia events, because the casino doors were right there. And on Vision after about 2 days of rotten weather, when all the smokers stopped going outside and only went into the casino, it became difficult for me to use the Centrum since it was funneling all the smoke into it. But on Vision the Schooner Bar was AWAY from the casino, so we escaped there, no problem.
That's my only issue, and I'm the daughter of a rabid reformed smoker AND I have asthma now almost certainly because I grew up with people smoking on me, and I cannot stand it. DH and DS do not react as vehemently (physically or emotionally) as I do.
Someday I hope Royal will be as brave as their sister line Celebrity, and put smoking outdoors
only.