Well, I'd say reliability is mostly based on the luck of the draw, it may be the silicon inside the chip that hasn't been manufactured perfectly which can lead to a shorter lifespan, or the manufacturer's production isn't perfect, or perhaps the design of the card isn't perfect. If we take a 7970 for example, the Sapphire Vapor-X card in terms of cooling shows very little difference to that of XFX's Double D design, they just offer different warranties/designs etc. If you want a reliable card (still using 7970 as an example), take a card which has good recommendations here (less so on Newegg), such as XFX, Sapphire, Gigabyte, Asus or MSI. Reliability and lifespan is mostly down to what stress you put it under, and the manufacturing process and testing of the GPU itself. Some may produce artifacts the first second you use it, others may die for no particular reason.
NVidia and AMD only make the GPUs and provide a reference design which is then sold to separate companies for manufacture. So long as you get a card produced by a trustworthy manufacturer and a good warranty, you'll be fine. I believe the most common difference between one card lasting 5 years and another card lasting 5 weeks is what has occurred in the manufacturing process of the making of the card, rather than the card design (reference or non-reference) by the companies that sell the cards to consumers.
Asus, Gigabyte, Sapphire, XFX, MSI are all good.