While I use a walker and not a wheelchair, I would recommend Celebrity 100%. They bend over backwards to help the handicapped people. We weren't able to get a handicapped stateroom or even see one for that matter, but all the wheelchair people appeared very happy. Doors in staterooms were wider, and very easy to open, and stayed open when pushed back.
Constellation Aug. '02
Second choice is Princess. Saw a post about Prisendam. Heard it was very bad after refurbishing,