Using Magical Express, renting a car, or using a towncar service are all good options.
Magical Express is likely to be the fastest way to begin having fun after you arrive -- because you can bypass baggage claim; you don't have spend timing renting a car; and you don't have to deal with getting your luggage to your room at the resort.
Rental cars are great if you plan to shop, dine, or visit attractions off-site. And, they're the best choice for someone who wants to be "in control" -- who doesn't want to depend on shared transportation at WDW.
For personal service and a sense of luxury to and from the airport, a towncar service is the best choice. Of course, once you're at WDW, you need to use WDW transportation (and/or take taxi cabs).
It comes down to a matter of personal choice -- and personal
budget.
The last time we used a rental car, we left it with the valet parking attendant when we checked in, and we didn't use it again until be checked out 4 days later. We're using Magical Express for our next trip. Then, for a F&W Festival trip with just my wife, we may opt for a towncar service, or we may use Magical Express again.
If all options cost the same, a towncar service would be my first choice. But with the excellent reviews that Magical Express has been getting lately, it's hard to justify paying over $100 (with tips) for a towncar service.