I've seen impressive things from both cards for BF, but in my experience the 280X is marginally better
In terms of future proof, I'm not gonna be a jerk and tell you nothing is future proof. However it depends on which brand of the card you're going with. All 280X are 3GB which will carry it's own weight better into the future with resolution/game requirements. However if you're talking about the 4GB version of the 770, then of course it's wildly the more progressive card. Albeit the 770 isn't quite powerful enough to utilize a full four gigs of video ram. EG the card runs out of steam, before it runs out of ram
If for the 2GB 770 vs the 280X I'd go price point for my decision, personally