Definitely faster to take the bus.
But if you do take the monorail from MK be sure to catch the "express" monorail, not the one that stops at each resort. Besides not stopping at the resorts, when at the TTC you just cross the platform to get to the EPCOT monorail. With the "resort" monorail you have to take an exit ramp down to ground level then walk up another ramp to get to the EPCOT monorail, so there's more walking involved with that option.