This is not even a choice for Dunmer, Nords and Argonians. Those two other alliances have ravaged our lands before we murdered their invasion force soldiers, Bleakrock is still under the Breton rule with no quests available to drive those n'wah out. No quests available to ravage those aggressors' land in retaliation, so what answer is expected here? Ebonheart Pact only for it is the only way left to revenge.

The Covenant fights to capture the Ruby Throne in order to restore the Second Empire - one of the Evils we, Dunmer, once defeated almost alone.
The Dominion seeks the way to reestablish Elven dominance over Tamriel - another Evil we still have to defeat along with our Pact friends.
Join the ranks of the Ebonheart Pact for we fight only to protect our national borders and freedom with no intent to turn other lands into our provinces. Keep to the Pact!

Victory for the Three.