As backer of both, I don't see how they could be more different from each other.
SC is the flashy "star and stripes" action movie; while ED is the "2001 Kubrick " slow tempo movie.
The first does not even exist yet; for now the only thing that exist is the flight model and fees implementations of damages and weapons. if you strip down Arena Commander, and put cubes; all that is left is cubes using the flight model , and a rudimentary shield/damage model, in areas that are really small and with limited number of players.
In the long run, there will be more, but as is now; that's what is there.
ED is a bit ahead; it has most of the mechanics done; the system jump mechanics, the instance mechanics, the damage and flight models, energy management and a basic AI and economy system. Overall is probably a year and a half (4 years in Chris Robers timeframe

) ahead, because decided to tackle the first person section and the planetary landing as extra/post launch module. It also does not have a single player story mode; which saves a lots of time.
I believe that they appeal to different kind of audience, just like 2 movies appeal to 2 different kind of audience (altho there are people that can mostly like both at the same level). I play different MMO for different moods; and space MMO games like SC and ED are exactly the same, so I cheer both of them, hoping that they will continue the tradition of their respective predecessors.