Epcot: Temple of Heaven
To take pictures at Epcot, without other guests in it, you should choose an area on the opposite side of the main entrance to watch the fireworks.
On most evenings the fireworks marks the end of the day and so most of the guests are leaving the park after the show. Now you may start taking photos of all the beautiful pavilions on your way to to the exit. Even the park security is very relaxed and gives you a lot of time to stroll around.