How do you define best? Will you have a car? What races are you running? Do you have spectators?
If you have spectators and are running the half or full. I like the Poly for spectators as they can walk to the TTC see you there, walk back and see you in front of the Poly after they exit the magic kingdom and then you can take the monorail to see them at the finish.
Boardwalk area resorts are nice if you are running the 10k or Full because you can spectate around the boardwalk.
For runners:
For the Expo I much prefer driving
For the 5 and 10k I've found driving is the most convenient followed by the buses
For getting to the half and full my order of preference is Monorail, Driving, Bus
For getting back to the resort after the half and full my preference is Driving, Bus, Monorail (and with monorail I much prefer poly because I can walk right to the room from the TTC rather than transferring and waiting in line again)