These are some of the main reasons:
-eVGA makes very high quality cards. The cards typically do not break down as much as other brands. Just on these forums alone, I've heard many less complaints against eVGA than say XFX.
-eVGA puts good stock heatsinks on their cards, making good overclocking possible. For example their 6800GT has the same heatsink as the 6800 Ultra, meaning it can easily overclock to Ultra speeds.
-eVGA has the "step-up" program. This means that if you purchase an eVGA card, you can use it towards the purchase of another card within 90 days. For example, let's say you purchase a 6600GT for $200 dollars. Within 90 days, you can ship it back to eVGA and use it as $200 towards the purchase of a 6800GT, just as Nubius did.
That's all I can think of right now. Does anyone else have anything?
Jesus said to him, "I am the way, the truth, and the life; no one comes to the Father but through me". -John 14:6