The express bus saves you walking to the front of the park, and waiting to go thru security & the turnstiles at the destination park; Uber/Lyft do not. In addition, for the MK Uber/Lyft would require getting to or from TTC or CR.
The advantage of Uber/Lyft are that you can usually get a car within 5 minutes, or 10 at most -- but the time saving may be lost because of the above points. They may cost less than the express bus, depending on how many times you plan to hop and how many in your party.
If you have children requiring a child seat, the express bus would be a better option.