JJ1217 :
I don't really expect how you want us to assess this. You haven't told us your resolution, your system, what you plan to play, etc etc etc.
The 770 is basically a glorified 680 being both cheaper and faster. It matches the 7970 Ghz, and beats it in some games. The 780 is maybe around 15-25% faster. The 770 is a better performance/dollar, but it really depends on how you use it. The 3GB of vRam on the 780 might be of more value to you. Its definitely a good card, and you'll be happy with either.
But before I would say to go for either, I would like to know what games you play, your system overall (to check if it won't bottleneck, and whether the power supply is enough), and your screen resolution.
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($199.99 @ Microcenter)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($29.98 @ Outlet PC)
Thermal Compound: Arctic Cooling MX-2 4g Thermal Paste ($7.99 @ Newegg)
Motherboard: ASRock Z87 Extreme4 ATX LGA1150 Motherboard ($144.99 @ Newegg)
Memory: Patriot Viper 3 8GB (2 x 4GB) DDR3-1600 Memory ($59.99 @ NCIX US)
Storage: Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive ($84.98 @ Outlet PC)
Video Card: EVGA GeForce GTX 770 2GB Video Card ($419.99 @ Amazon)
Sound Card: Asus Xonar DX 24-bit 192 KHz Sound Card ($77.98 @ SuperBiiz)
Case: Cooler Master Storm Scout 2 (Black) ATX Mid Tower Case ($59.99 @ Newegg)
Power Supply: Corsair Enthusiast 750W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($99.99 @ Newegg)
Optical Drive: LG UH12LS28 OEM Blu-Ray Reader, DVD/CD Writer ($74.94 @ Adorama)
Operating System: Microsoft Windows 8 (OEM) (64-bit) ($87.98 @ Outlet PC)
I plan on maxing out games like Battlefield 3, Crysis 3, and Far Cry 3 at 1080p.