For me its .308 because

1. I don't need to make real long shots with it.
2. I could get it in a short action custom compact Winchester 70 Rifle that doesn't weigh much.
3. Its cheap to reload for.
4. Its easy to reload for.
5. It kills just as well as most other 30 caliber cartridges at under 300 yards.
6. Did I say it was light and easy to carry?