First you have to decide whether you want to mount it in the conventional position over the bolt, or in the forward position on the Picatinny rail. If the latter, then you will need to go with a special scope designed with a long "eye relief." Leupold and others offer scopes with long eye relief. These scopes are usually lower power (4 or less) to give you a wider field of view. If you go for the conventional mount, then the power will depend on what range you are likely to be shooting. If most shooting is less than 75 yards then a variable 1-4 power is fine. If you think you may be shooting at distances up to 150 yards or more (which the .308 is quite comfortable with), then a 2-7 variable or even a 3-9 variable would be good. In terms of brands, Leupold is great, they offer a huge variety, and their customer service is similar to Ruger: fantastic.