I lived at Vista, so I would run around the complex. It was pretty nice and a good amount of shade even when I ran later in the day. A loop around the complex was approximately one mile.
When I wanted distance I would run from Vista to Patterson and back. It's about a mile to Little Lake Bryan, 2 miles inside passing both Chatham and Patterson and back out, then another mile back to Vista, so 4 miles total. The mile to Little Lake Bryan can be really sunny, so you'll definitely want to save that for mornings. When I'm training for half marathons, I'd do the trip to Patterson and back twice and then run just outside of Vista Way (near the Vistana resort--nice and shady!) until I had finished the mileage I wanted.
My favorite resorts to run at are Boardwalk and Coronado springs! Swan and Dolphin are also really nice to add onto a run at the Boardwalk (very shady). I love running the resorts!!