Western digital is more reliable in my personal opinion because of the following:
1. I've never had a western digital drive die on me over the years
2. They run cooler than seagates
3. They run quieter
4. Western digital RMA process and support is great(I've sent drives in that I suspected of problems, but never actually failed.)
Seagate is the cheap way to go if you want to save money and don't care about data loss.