ORIGINAL: bwheeler
I would lean towards the .308 due to reload options and cross-sect. density.
The most commonly used bullet in a .243 weighs 100 gr. The most commonly used bullet in a .308 weighs 150 gr. The sectional density of a 100 gr. .243 is .242. The sectional density of a 150 gr .308 is .226. I thought higher sectional density was better.