Universal was far superior than Disney when it comes to handicapped individuals from experiencing the "magic".
I traveled with someone in a wheelchair who had suffered a stroke. We were able to ride all rides except one. We went on the Mummy, however, it is really far too violent a ride unless someone has enough strength to keep themselves in the seat.
On Men in Black, they attached his wheelchair to a platform that comes out of the floor. When the car comes around, they slide out two of the three back seats and slide the platform with the wheelchair in. The let us ride twice in a row as it took about 5 minutes to get him strapped in.
Back to the future is also pretty violent as far as the moves the car makes. I wouldn't recommend this ride for someone in the physical condition I described above.
MGM studios wasn't too bad either. However, the Magic Kingdom I felt was pretty lousy regarding wheelchairs.
Just my thoughts,
Steve aka Fritzie