Well, you have to chose 1 side, and any of the 2 can win. Normally I'd say Dawn, because Dawn used to always win on every servers, but Dusk started to win lately on a couple of servers.
To subscribe to 1 side, you have to go talk to the preist of that side, on the first week of the competition. It's easy to notice weach week it is, just by going to town, the first week the town is normal, the second week there are ghosts in town (Orator of Revelation) that never stop saying the same thing.