Just let me add my opinion to this. Western Digital always, Seagate never.
I say this not from a performance perspective but one of reliability. I work in tech support for a major retailer and pretty much every laptop I have ever dealt with that had a faulty hdd was fitted with a seagate.
On a personal level, the only drives i have ever had fail on me personally have been Maxtor and Seagate. Yes they exchange them without a quibble but all the data is gone (I do backup, but still annoying).
I have never had a WD fail, all my techie colleagues also swear by WD and hate Seagate. The repair company we work with also avoid Seagate if they can. Just not reliable.
Just my limited experience but thought it should be pointed out that better performance is no good if it breaks all the time!