We've used both Walker and Apple, and been happy with both. We had a better customer service experience with Apple, but no company gets everything right 100% of the time, and Walker did offer us coupons off our next rental. If you don't have time in your schedule to meet a rep from the company, you may want to choose one of the companies that's authorized to drop off equipment at your resort. (The list is in one of the stickies at the top of the board.)
The Disney drivers, without exception, have been absolutely wonderful, polite, and helpful to us in getting on and off buses, boats, and monorails. I half-expect them to wear big coats and hats to hide their wings and halos. Even when able-bodied passengers copped an attitude, every driver I've met has been great. WDW was the first place I ever had to drive an
ECV (broke my foot checking into the resort), and for the first couple of days they all volunteered to steer me up and down the ramps until I got the hang of it, and all with a sympathetic sense of humor. Whatever they're getting paid, I'd love to see them get a raise.
Also seconding the recommendation of taking a practice run at a grocery or big-box store. Their ECV's tend to be bigger and clunkier than the Orlando rentals, so if you can master them you should be fine! One skill you'll need is the quick stop. because people WILL run out in front of you as if you don't exist, and then blame you if you can't stop in time. I recommend putting something tall like a flag on your ECV so there'll be soething at people's eye level.