We have done both, and both have their own positive spins.
Personally, I would say that I preferred the Magic Kingdom one over the EPCOT, but only slightly.
MK: They take you all around the lake in front of MK and show you some of the sights. You have a panoramic view of the castle and the fireworks. More like a wide angle view as if you are watching it on TV. It looks amazing.
EPCOT: Our driver took us around the route of the water ferries so we could see HS, Boardwalk, and Beach Club. You dock under the Bridge where you enter the International Gateway in EPCOT. It does feel more exclusive, in the sense that you are inside of the park. With that said, you are inside the park, so viewing is not as dynamic.
Both were worth the money in my opinion, so you cannot go wrong!