I like either Budget or Alamo. We arrive in Ft. Lauderdale first to visit family, then drive up to WDW and return car after we check in. We rely on WDW transportation while there. Esp with car rentals being so expensive.
I like those 2 companies, because I've never had a problem with them, they seem to have the best prices, and they have car rental desks in WDW, making it very easy to return the car on property for us.
We reserve using the Costco.com site- Travel link. They offer discounts and bonus coupons, like $25 or $30 off rental. Mousesavers.com has some discount codes out too.
Rental rates change all the time. So just reserve something with your preferred company, then keep checking rates. If a cheaper rate becomes available, you just have to phone and ask for your rate to be adjusted. If It's with another company- you can cancel & re-book.
Some have had good luck with Hotwire- but it's pre paid, so if rates change, you're stuck. I'd save that option for last minute booking.