Seagate Barracuda 7200.9 300GB 7200 rpm 16 MB - $119 CAD or
Seagate Barracuda 7200.10 320GB 7200 rpm 16 MB - $115 CAD
i think is pretty clear...the second bigger hdd .... new technology (perpendicular recoding) allowing bigger data density and less platters used to store data...this means less noise and heat dissipation.....
i would go for a WD drive ... the big seagate drives are very noisy....(in seek mode they make a very loud noise ... while WD drives are extremelly quiet)...
I'd stick with the Seagate due to the longer warranty. 5 year versus only 3 year with WD. I will say that Seagate and WD are the only two brands I completely trust however.
As for the 320 versus the 300, it's really a no brainer. The 320 is bigger, newer and less expensive. What's to ponder here?