If you get the bus to the CR, you will be able to just walk over to the MK...about 8 mins along the sidewalk that runs underneath the monorail line. If you take the Polynesian or GF bus, you will have to either take the boat or monorail to MK..that can take a bit longer since you have to wait for the boat or monorail to arrive.
If it were me, I would go with the CR but any of them will be fine.