Since you require access to both MK and Epcot, I would suggest OKW. The reason is the larger accommodations, and the easy bus access to both locations. If you stay at VWL, you will have much easier access to MK, and can do an easy bus to Epcot, so that would be a close second for you. If you stay in the Boardwalk/Beach Club area, you will have excellent access to Epcot, but there have been many issues reported about bus service to MK. Also, with the "down and out" design of OKW, it feels more like a home, so your kids might settle in better. We have found this to be the case when we have had little ones with us.