Not sure about John Deere, but I have a hydraulic self leveling loader on my 7520 Mahindra and while it is nice to have, I wouldn't get it again. It was an extra $900 for me back in Dec 04 and I have not gotten my $$$ worth out of it and don't see myself getting my $$$ worth ever.
I suppose that if you were using your tractor for unloading trucks and moving pallets of material all the time then it would be a good option to have, but for the occasional unloading that I do, it was $$$ poorly spent.
One other thing, by chance is the self leveling feature on the John Deere able to be turned off and on? Mine is on all the time and was a hindrance for a while until I got used to always curling the bucket to keep the dirt in. I believe that M series Kubotas have an on-off switch for theirs. I would be happier with mine if it had on-off capabilities.
Good luck with your decision, oh by the way, what does Deere charge for their self leveling feature?