In terms of toughness and overall durability, I haven't found anything I think that can match AI. Their machine tollerances are also second to none. (any AI bolt can go in any AI rifle, and work. Can't often say that about a custom job.)
You can beat the rifle to hell and back, and it will still shoot, on target, with no affecting accuracy.
All that said, I bought an Armalite AR-30 in .338 Lapua Magnum for 1/4th of what an AI costs.
.338 Lapua and .308 Win are pretty different.
.338 Lapua has over twice the range, and muzzle energy, of a .308.
Now, .308 with good loads is effective out to 800-1000yds.
.338 Lapua is effective to ~1600-2,000+yds
.338 Lapua will also beat you up much harder, requires use of a muzzle brake, and costs sixty bucks for a box of 20. (on the bright side, it's awesome match quality ammo.)
If you're going to be shooting beyond 800yds much, .338 will do you well. If not, you might as well get a .308 and shoot it more!