Have only been to the World twice but so far I'm a big fan of the Magical Express. Each time was less than an hour from landing to check-in. Could a cab be faster? Perhaps. But for me, avoiding the hassle of getting my luggage, dragging it around the resort to my room, the expense of a cab, and then having to arrange transportation back to the airport, is easily worth that wait and more.
I've also found that ME actually is a great way to shift from the stress of airline travel--I spend more time waiting around there than I do for ME, certainly--and into vacation mode. All the passengers are excited (or at least relieved!), there's a "welcome" movie, and some of the ME drivers are very entertaining. On a trip earlier this month our driver, Tim, regaled us with Disney trivia (such as the length of time it would take to stay one night each in every room on Disney property) until it was time for the movie to start. He was a lot of fun and it was a great beginning of the Disney experience for us.