Both companies are very well respected , they both have high quality products and if they have similar or equal products then all comes down to price (at least that's what I used to do all the time).But recently there have complaints against Seagate drives of dodgy firmware, bricked drives, and massive data loss.
Moreover after Western Digital RE4-GP, the first Enterprise class drive with Dual-core, 64MB cache and intelligent spin-management technology why go for Seagate?
Regards
Aditya