Are you asking whether to get one R9 280X vs 2 GTX 770s?
Generally the consensus is to go with only one card. If you already have a GTX 770, I would say get another. If not, I would say either is great, but depending on how many monitors and the resolution you play at, you might want to consider the 280x. If you're willing to get 2 GTX 770s, why not just get a GTX 780 or 780TI and SLI later if you need to?
no ONLY ONE card
i don't have any good gc now
i want to play on one monitor
one r9 vs one gtx 770