I went with Order being more populated. My reasoning is basically from WoW examples. Alliance is almost much higher than the Horde in most servers lol. Everyone wants in on the "Good Vs. Evil" action. Not me, I'm a bad guy in a nice guy's body lol.
I found that the "good vs. evil" wasn't the issue with WoW early on; it was the "12 YOs want to play hot looking elf chicks" syndrome.
I quit for a few months and, when I came back, I found a lot of my old guild members had re-rolled Horde, so I did so. There were so many more mature people on that side than on Alliance.
I think the children (emotional years, not calendar ones) are going to end up Destruction because they look cooler, it (imho) has been pushed more in the videos/trailers that I've seen, and they've got the ezmode toon (squig herder).
The only thing worse than long queue times due to overpopulation is sitting on your bum waiting for a group to fill out. *shrug*
Moonrunner: Tnakswhisper 70 NE hunter, Tinymighty 70 gnome warlock, 61 NE priest
Norgannon: Tnak 70 BE priest, Blackwater 70 BE mage.
both: assorted lvl ones in Orgrimmar, Ironforge, and Booty Bay. My level ones twink out my playing toons. Gawd I love the auction house!