SATA is the future, so it’s always worth it to upgrade to future technology. Unless you will be buying high-end drives like Raptors, RAID will get you nothing that’s noticable in every day use. RAID-1 is, however, very secure and redundancy is always a great idea.
Right now, 160GB drives are cheap and plentifull, generally your best value per GB. Don’t skimp on entry-level drives, get the best that the drive makers offers. In the case of WD, that’s the JB series for standard IDE drives. Like THIS . Or, the JD series for SATA, like this .
The Seagate drives are also well respected fro reliability and performance.