
Have never used either, so your opinions matter. I like free but I also like to have my luggage with me, also going from airport right to resort without any stops sounds appealing to me also.

Maybe I have already made my mind up
If you use a towncar service, you'll have to go to baggage claim at the airport. There, you'll wait for your luggage (and wait, and wait, and wait...) Also, you'll have to wait while the driver retrieves the towncar (because towncar drivers can't leave their cars parked at the curb).
If you use the Magical Express, you'll bypass baggage claim. You'll have to check in at the desk, board your motorcoach, and wait for it to be dispatched. You might travel non-stop from the airport to your resort, or you might have one or two stops (possibly even three stops) at other resorts near your resort.
On average, neither service is much faster or slower than the other in getting you to your hotel.
I like letting Disney handle my luggage at the airport and at the resort (with Disney even paying the bellman gratuity). I like comfortable motorcoach seats for all four us in the family (rather than three of us stuffed in the back seat of a towncar). I don't mind the possibility of briefly seeing another resort (or two or three) on the way to our resort. And I like free.
Some others prefer the personal service of a towncar. They don't mind waiting at baggage claim. They don't mind tipping everyone who touches their luggage. And, presumably, they don't mind the cost for the towncar service.
It's a matter of personal preference.