Should have been. .308 over .338 is good advice.
The .260 is a perfectly fine cartridge for the AR-10 platform and factory ammo does a very solid job. The 7mm-08 is also a consideration.
Of the .308 family, .243, .260, 7mm-08, .308 and .338 Federal, I might put the .338 ahead of the .243. Then between .260, 7mm-08 and .308, it is kind of preference if you toss out the prevalence and cost of factory ammo benefitting the .308.