It would depend on if you were going to just do the Disney theme parks or also wanting to do other things in the Orlando area. It would also depend on the room rates at the various on-site and off site properties.
If this will be your first stay, only going for 3-4 days and are going to just do Disney then I would stay at a Disney property. If you are going for longer or want to do other things than Disney then I would stay in a Downtown Disney property. You get the early opening perks and are within walking distance of Downtown Disney. It is also easier to get to Sea World or Universal Studios.
To get the "full Disney" experience then stay at an on-site Disney hotel. It really is something the others can't duplicate.
Hope this helps
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