Like as far as ratio of players.
Apart from anecdotally based evidence does anyone even know for sure if their realm is one more than the other?
From the pre-launch reddit survey responses and a few people on the server Discord running Census addon, it seems to be roughly 70/30 for Alliance.
One of the Atiesh Discord mods is running a census addon, and it looks to be 70/30 A:H right now.
13000 Alliance characters.
5500 Horde characters.
As of his last post update.
This ratio means that Alliance might have a slightly easier time finding dungeon/raid groups, while Horde will have faster BG queues, once BGs are implemented.
New count:
Alliance: 30,100 characters.
Horde: 20,000 characters.
As of last night:
Alliance: 74,117 characters (10, 969 of which are level 1’s)
Horde: 35,726 characters
Of further note: According to testing done by WarcraftRealms, generic /who commands now only give results for people in your own layer. If you do a /who on a specific player, you should be able to get a result without regard to layer though.
Then Blizzard directly contradicts the claim: