There’s obviously but two options here. Each server has its own population dynamic but I think the following are fair generalizations:
- Population. There seems to be more Alliance than Horde so if you roll Alliance, your BG queues will probably be longer.
- Gear: It seems to be easier to gear up an Alliance toon due to quest rewards (although Horde casters may have it a bit easier). This means if you roll Horde, you’ll probably loose more BG’s than if you rolled Alliance. There’s an older thread comparing quest rewards…still looking for it.