At 1080p the 770 is a good solution for 3 years or so. Anything higher than that and a 780 would be a better solution. So it really depends on your resolution.
As far as money wise what is the best to do it kind of washes out as when you upgrade you can sell your old card, and obviously a 780 will go for more than a 770. It matters how much money you want tied up in your computer.