Well in my opinion, Me and my brother played the first empire at war and the expansion as well. We got to the point to where we couldn't stand ground fights anymore and we wanted to just share the galaxy (split half, and half). We would amass huge space fleets we would take turns who has the level 5 space station or not. Well we noticed the game was like paper rock scissors!
Empire > Consortium
Consortium > Rebel
Rebel > Empire
At least that stands for space fights only.
My reasons to back up my claims.
well the empire has the deathstar which i do recall it has a nice constant spawn of ships and all the empire needs is a bunch of SD's and other ships that unload smaller ships and have them just sit backand guard darth vaders rear while the smaller ships attacked/defended the front of vaders ship.
MEAN WHILE whatever you build up as Consortium in the end you will be defeated no matter what... I had taken out vader, and all his cruisers but by that time my fleet was little to none then the death star (while we were fighting blew up my space station) it was just a fight i already knew i lost as soon as we started. I have never won against my brother has Consortium.
Consortium V Rebel is more of a fair fight, and to us we enjoyed this one... tactics are more needed but we dislike both of these factions (wish we could do empire V empire) :P
But im sure you understand the rest and what not, if you would like later i could go on about the other faction fights we had.