I'm with Florida Mobility Rentals this time, and it's been fine. By far the cheapest quote I had - and I could have had the extra rear basket on the back for only $15 for the entire 2 weeks! Some places charge that per day!!!
Incidentally, while Disney say only preferred vendors can leave scooters with them, when I went to the luggage section at AoA and said I was waiting for a scooter, they said that one hadn't been left for me yet. I said it wasn't a preferred vendor - and was told 'that doesn't matter'!!!