From the viewpoint of a player that wants to play as evil aligned character, I can see 2 choices.
Play as demon, get access to extra bonuses that come with demon races, eclipse raid fun time, and other demon gimmicks.
Other choice is play as human, go evil, but have bit more freedom about where you live, and an option to join guilds that can control cities on Syndesia, a planet that will be most busy with traffic, as all races will often travel to there. Also you can have good human and evil human in guild, which can lead to some nifty commerce tactics, working with Tartaros and Arboreus.
So I see demons as a great choice for (evil) solo PvPers, and (evil) guilds that mostly want to raid and pillage. Meanwhile I see evil humans as a better choice for (evil) guilds that enjoy GvG combined with control of the lands, more developed commerce and things like that.
(I don't know a lot of details about abominations yet, so for now I'm not considering them)