Well EVGA 680 is top class, but what your final decision will be depends on what use are you gonna make to your pc. 680 outbids 670 and the price difference is big. If you are going for hard gaming I believe you should go for the 680 (I am in love with it BTW ). Comparing the two (ZOTAC and EVGA) I would stick to the EVGA not just for the brand but in terms of gpu capabilities as well. Though the human will not notice at all the difference in performance between the two gpu's I would give that extra 20 bucks to get a theoretically better card.
Plus the EVGA comes with a backplate which provides structural support and more effective cooling!
Both the 680 and 670 perform so well on 1920x1080 that you won't be able to notice the difference. For benchmarks, the 680 is only slightly better. The price difference is pretty significant, so the 670 will give you much better value.
My MSI GTX 670 PE sits at 1350MHz Core (+600 Memory) stable thanks to unlocked voltage. That means it's not only faster than stock GTX 680 but faster than most overclocked 680s as well. All of this without going over 65'C at full load. Getting a 680 isn't worth it imo. Your best bet is to buy a MSI Power Edition 670 as they have voltage unlock support through AB. That's something EVGA doesn't offer for their 670s and charge an extra $200-300 for with their 680s.
81fps in Uningine @ 1920x1080; Normal Tesselation; 4xAA