First of all, Coke and Pepsi preferences vary depending on which area of the country you are from and Anaheim happens to be a more Coke-leaning district from my understanding, so all the locals on here cannot really speak for everyone when they say Coke is more preferred.
What Disney needs is a flavored Soda...I know Dr Pepper is probably out of the question but that's my personal favorite. Of course, I'd take a Pibb if they had it (I believe that's a Coke product) or at the very least a Cherry Coke...the old cola flavors get old to me after a while. That's my one biggest complaint about Disney is the lack of soda variety.
What would be awesome is if they took a cue from Universal Florida and started adding those freestyle machines...then lots more people would be happy!