Once we started flying, we used the Magical Express and loved it. It made things so easy in that, we exited the plane and headed straight to the bus. Of course, we loved the original program that showed on the bus as opposed to the current one. Then, we used the onsite bus system within WDW and then took the Tragical Express back the airport at the end. The bus system really did help us in that we didn't need to rent a car and didn't have to deal with traffic. I am unsure about the train situation, including how frequently the train will arrive/leave at the airport, how many people will be carried each trip, and how many trains will service WDW. I have long thought that a light rail system to/from the airport with two tracks and tying to Disney Springs or another central point would be efficient but definitely have some questions.
In recent years, I have started renting a car from the car rental site by the Grand Floridian and still used the Magical Express to/from the airport. This provided me with more freedom as we go to grocery stores for supplies and also could drive to UNI/IOA and to Epcot/Studios/Animal Kingdom far more efficiently than using the WDW buses. Going to the Magic Kingdom was better with a bus since we wouldn't have to use the ferry/monorail. Using a car for everything else made life much more easy and eliminated having to wait for a bus after a long day at the parks.
Still, I will miss the Magical Express as it made life easier but maybe the trains will be just as nice.