not talking mixing them or anything else, if you had to pick just one hard drive what would you pick of the 4 and why?

300GB Western Digital VelociRaptor (10K RPM) (16MB Cache)
1TB Western Digital (7200 RPM) (16MB Cache) (SATA)
500gb Western Digital (7200 RPM) (16MB Cache) (SATA)
64GB Solid State (by: OCZ)