When are you going? Caribbean Beach will be closed down from Sept 8 to mid December so that they can redo Old Port Royale. There are several other moderates to choose from though like Port Orleans Riverside, Port Orleans French Quarter and Coronado Springs.
Ive stayed both on and offsite and I much prefer being onsite because you are immersed in the magic 24/7, its much easier to get to the parks, and I just find it more relaxing. I would never stay offsite again unless it was a quickie weekend thing and I ABSOULTELY could not get onsite anywhere.