You ask a good question, but offer no criteria to base an answer on. However
, I will offer one anyway:
One rifle, one caliber, I chose .30-06. Of your choices, I would choose .308.
Reasoning:
1. You can get ammo anywhere, which implies both availability and competative pricing.
2. The range of loadings for these calibers boggles the mind! There are sabot rounds that I use for varmint control and hunting rounds of various configurations suitable for all North American game. There are also available AP and tracer ammo for tactical situations
3. Both calibers have many choices of platform (rifle), from military surplus to custom hunting rifles.
Is a .308/30-06 the best choice for every situation? Of course not, and may, in fact be a poor choice for you. Never the less, except for shooting birds on-the-wing, there is little that cannot be done, and done well by either of these.