7950 is definitely a better buy price/performance-wise, but I bought my 7970 because it was just so tempting. At 1080p you wont notice a difference between the cards, but you absolutely need to overclock 7900 cards. If you wont overclock then a gtx 670/680 would be a better choice.
I have the HIS IceQ 7950 (the Turbo model of which is rated highest in performance on TH among the 7950's, the only difference being that it comes factory OC'd to 900Mhz) and I'm not disappointed at all. I have it OC'd to 1000Mhz/1350Mhz (temps stay under 60ºC w/full load) without any voltage adjustment which is almost at the level of 7970 but for $110 less. Boom.