Haven't stayed onsite but have been there. You will find the onsite hotels are very close to the parks, (for Orlando!). Between 5-10 minutes walk.
We didn't stay onsite - we drove there from Disneyworld - parking was easy.You park near the City Walk, which links the two parks. Depending on when you are going, you will be able to see most of the parks in a day, possibly two. In January (very quiet) we rode all headliners, some more than once, took in several shows, ate, spent plenty of time in places like Seussville, and were still all done with both parks in a day.
that might help you decide how critical on or off site location is