GTX 770, it basically a overclocked GTX 680 and GTX 680 outperforms 7970 at stock.
NVIDIA's $400 price point is a great choice for taking this segment by storm. With current pricing, AMD is not competitive at all. The Radeon HD 7970 is slightly cheaper, but much slower, and the HD 7970 GHz Edition is more expensive and slower although i have noticed you can get a few 7970GHz models for roughly 400ish now. Both AMD cards also lose to NVIDIA's recent offerings when looking at power consumption and noise. The only thing AMD bring to the table is the rich Never Settle game bundle which if you're thinking about buying those games might be worth it to consider the 7970.