I would probably rent at WDW.
I-4 is a disaster, so I would probably avoid it for the 25 bucks. Although the disaster is a little further north the WDW. Plus these rental cars with their license plate paying toll tags and their convenience fees, and there is tolls on some of the routes from the airport to WDW - so that will chew into your 25$ savings A LITTLE.
You can rent a car at the car care center, and gas it up when you return it, only issue is depending on where you rent the car on property, you have the hassle of getting back to the hotel for the magical express. I have rented cars from the car care center (near the Polynesian) and there was a courtesy shuttle, but I would probably return the car and just take a lyft back to the hotel at this point in time.
Plus, it does leave you the option of maybe picking it up on day 2, or returning it a day early perhaps, if thats something you want to do and save a few $$.
However, the biggest hassle of an airport rental (in my eyes) is the handling of the luggage, and that is negated by hotel-airport checkin when leaving, and EVEN if you do rent at the airport, I would still register for ME so they grab your bags at the airport upon arrival.
To me, renting at WDW would be less stressful and the way I'd go. Whomever is the first one packed to leave can go return the car while the other one packs/watches kids.
ETA: I actually like the ME. They have a disney video playing that the 5 year old will probably like, the seats on the bus are comfortable. To me its kind of like a preshow before getting on the main attraction.
my 2 cents.