Both side are active, which is comforting. Like the OP, I always worry about activity when making a new character or starting a new game.
For myself, I picked Exile side. I spent a week playing throw away alts on both, getting use to the game mechanics and helping me pick a class. I ultimately decided Exile, not because Dominion was dead but because during the hours in which I am normally active (after 9pm PST) there seems to be more potential people on. There was still players dominion side, but Exiles had the slight advantage in "RP potential" based on the two characters I finally decided on. I still have my Draken planned for the Dominion side as a back up or for when I need a break, but right now I'll be on my Granok on the Exile side.
That doesn't make the Exile side "better" for RP. Everyone's situation is different based on the times they play and their expectations for RP and interaction. For me and mine, the Exile side inched out ahead of the Dominon side; but not by much.