There is no "regular" shuttle from MCO to WDW. Over the years Disney has worked with Mears to shuttle people but I understand that the contract ended and Disney is considering going into the shuttle business themselves in the future.
Anyway, we used Mears once and will never do it again. You may get lucky and get on one of their vehicles and go right away. Other times they wait for more flights to arrive. In either case they will stop at any number of other hotels including yours. It can sometimes take a LOT of time. It's also aggravating and IMO a terrible way to start a wonderful Disney vacation.
Although a town car is more expensive for two people it is much more relaxing and they will take your luggage for you and then take you straight to your hotel (unless you want to stop at a grocery store along the way).
There are a number of quality towncar services. Keep reading these boards.