Hey-
When you're staying on-site, the Disney internal transportation is great... and almost always available.
I know in our experiences, a lot of the off-site resorts have shuttles a few times in the morning and a few times at night for pick-up. I would be sure you call them directly and find out the shuttle schedules before settling on a hotel. Staying off-site can save quite a bit of money depending on the time of year. I think it comes down to what works best for your family?
Happy planning!
xoxo