If you know the majority of your trip is going to be at the MK - go with VWL - the bus tranportation from BWV to MK was some of the worst - all the epcot resorts were on the same bus - and since BWV was last - we had to stand.
Now however if most of your time will be spend at Studios then go with BWV.
If you go with VWL ride the boat to the Contemporary, then ride the monrail to the T/T, change monrails, then ride the monrail to Epcot - kids really seem to want to do this again and again - they really like the monrail ride more than going to the parks. Of course if you want to do this parks - this could be a problem.