We've used Amtrak for the last 10 trips and we always detrain in Kissimmee. Orlando is a mad house, about 200 people get off here and its a mad scramble for taxis, and luggage. Boarding here is worse, a long line of people trying to board through the single car door, all the while baking in the Florida sun. Granted most get on and off here because they do not know that the next stop in Kissimmee is about 20 minutes further, small station, Old Town Kissimmee only about 10 people get off, real easy to catch a cab to WDW. Easier yet to board to go home, same amount get on and by the time you're settled in your seat, you're at the Orlando station where about 200 people are trying to get on. We just sit and watch out the window, this stop is about 30 + minutes long. Be it as it may, from either station you can get to WDW, but we "always" detrain and board in Kissimmee.
We catch a cab, usually 4-5 in a cab line or the station master will call one for you. Fare from here to MK loop of resorts runs us 35-38 bucks plus tip, about a 15-20 ride. I have seen taxi vans there also, same price as a car taxi.