Best is somewhat subjective because a vague inquiry can result in the people answering the question bringing their own needs/values to the plate. I can tell you that in practical LR competitions in the Rockies, .260 Remington (and substantially similar 6.5mm cartridges) and 7mm RM/WSM have been dominating for the last four years.
.308 is at a handicap compared to the cartridges that are popular for practical long-range shooting. At the 08 and 09 Steel Safari, the high .308 was in 7th place both years. They had 75-83% of the score of the winner, who was shooting a 6.5mm or 7mm cartridge. This tells me that a .308 shooter with a great rifle and shooting at the top of his game is still at a significant disadvantage compared to a comparably-skilled shooter using .260/6.5-06/etc or 7mm RM/WSM/etc.