I am planning to get a new hd 7950 and the above two are the only ones available to me. I think the vapor-x looks better, but I heard that due to bad cooling it reaches very high vrm temperatures resulting in crashes. And I have never used a gigabyte card before, so I don't know much about it.
I have the Gigabyte GTX 670 windforce and it is great. Idles around 28C, playing COD games maxed out for a few hours, doesnt get about 40C with custom fan curve and i have pretty good case cooling too... Not sure the heat difference on AMD would be though, but this is my first gigabyte (always been an evga fan) but i would definitely buy another for SLI.
Can't really compare the same cooler on a card that uses entirely different processor architecture and board design.
All in all, they are both great coolers, but I think Sapphire wins this one by a thread. Whatever you heard about the Vapor-X was probably just caused by a damaged or malfunctional product. It happens to pretty much every manufacturer out there from time to time, but all I've heard from Sapphire is good.
And like you said it looks much better. I think Gigabyte design looks rather cheap and feels pretty flimsy overall.