Bus or boat from MK... The bus should also drop you off with a short walk to Trail's End. I personally prefer the boat as I feel it is more relaxing and you get to see more than if you took the bus... nice views of MK, CR, WL, you can wonder what that shipwreck is on that island in the middle of the lake (I think it is still there), and the now closed River Country. Also, if the weather is nice you can sit in the open air areas.
Taking the bus you get to see CR parking lot, MK parking lot, the sign pointing to the entrance to WL.