Hiya Jill!
Thank you so much for stopping by! While I can't say which is the best place to rent and Electronic Conveyence Vehicle (ECV), I can let you know that there are a few different options, and I can hopefully help you make the best decision for your vacation based on this information.
First of all, you can
rent an ECV from Walt Disney World Theme Parks, Water Parks, and Disney Springs. While the daily rates are the same, the deposits for the Walt Disney World Water Parks and Disney Springs are a bit higher. Please keep in mind that these ECVs stay at the location they were rented at, so they cannot be taken to the bus stop or your Walt Disney World Resort Hotel. Rental cost does transfer from park to park, but ECVs are rented on a first come, first served basis.
You can also rent from a Disney Featured Provider-listed on the webpage I've linked up above-and you'll have access to the ECV around your resort and beyond! Disney Featured Providers will drop your ECV or other mobility device off at your resort, and once your vacation is over, they'll pick it up there as well. They do offer some other great services such as in-park replacements if something goes wrong.
Hopefully one of these options will fit your needs!
Have a magical vacation!
Amanda