1) Depends on the region : EU or US
2) Depends on the day of the week
3) Depends on the time of the day
4) Vary so much that you can say either Alliance or Horde, and that someone would say that you're right ....
During the daytime I think it's pretty balanced, but the evening though is a different story. Alliance wins pretty much every BG in the evening, unless you get in a group with the Russian horde premade, lol.
