I vote for Apple. They have been more than willing to work with me even when I had a problem with my personal scooter. They went above and beyond trying to help me correct the issue I was having. We have also rented from them and it was an awesome experience!
I also think that they rent their scooters for less than anyone else and will also give a Disboards discount if you mention that was where you heard about them. I believe that is is around $150 or less for their scooters for a week.
Just as an FYI, if you want one for ease of putting in or out of a vehicle, then stick with a travel scooter, unless the weight of the person requires a bigger scooter.