I'm told overheating is the main cause of a GPU's demise these days, keep your cool, keep your GPU. But what brand is best known for making durable GPU's? ATI or NVIDIA? I'm hesitating between a 5870 or a GTX 680 personally...
The best thing you can do is find a card with a good warranty and easy RMA process. Certain cards will get hotter than others my old Radeon 4850 comes to mind, that thing actually got to like 90C if you're really that worried about it, buy a brand that already attached an aftermarket heat sink for you and warranties it against defects.
To make the matters worse, besides the chip maker, there is also the card manufacturer: Gigabyte, MSI, Asus etc. But honesty, it does not matter. Take the one which offers best performance for what you do. There is no real longevity difference between GPUs, or at least no study comparing it.
I too would suggest this comes down to brand (as in EVGA, ASUS etc). Overheating means inferior cooling which comes down to fans on most cards. Some of the top range cards use 3 fans across the board length and they expect you to over clock them. Another factor rather than overheating is the noise the fans make under load.