it's really hard to decide which company has the best quality since we don't have the money to buy every vendor and use it until its death... different ppl had different experience with different vendor... there are some ppl who use good brands like msi, asus and gigabyte but their card died in less than six months... some ppl who use not so quite famous globally like sparkle, pny, palit but it still usable even after 2 years... maybe these company should be classified as follows...
best service quality - evga
globally recognized vendors - msi, asus, gigabyte
good as well but market share not as huge as it seems - pny, palit, gainward, zotac, sparkle and so on...