I've never gone over through the Toy Story lot and gotten on a bus there from Worldmark. While there's always a steady stream of TSL busses, those are also ART busses contracted to run for Disney, so in my head, that's walking further to get on an ART bus vs. the closer one I could use from Worldmark.
The difference between the ART shuttle and the TSL shuttle is $$$. One cost and the other is free.