western digital is usually the best brand, however you might also want to check out other features
look at the RPM to make sure it is good enough. 7200 is standard for desktops
look at the cache. More is better, 16 is standard but 32 is becoming more popular
also look at ide vs SATA. Ensure you are getting one that matches your computer. If you have both, go with SATA as it is faster