from what I can find online it appears that staying at the Riviera resort would result in the shortest travel time to Epcot except for maybe staying at the beach or yacht clubs. It might even be about the same amount of time to walk from the boardwalk as taking the Skyliner.
Skyliner would be the fastest. It’s quick. Even if they slow or stop for some reason, I think it would be fastest. The only kicker is it puts you at the International Gateway of course.
Did it this week. Walking shortest from BC/YC/BW but 2nd would be gondolas…mostly because U may have to wait for gondola either coming or going peak times