Seeing as most harddrives can't fill even the ATA100/133 interface, it doesn't really matter. If you see a good deal on a PATA harddrive, don't be afraid to buy it. If you have a newer motherboard that has only one IDE connector, then you probably want to stick with SATA.
PATA (IDE) is dying and disappearing, if you get a PATA drive now then you risk not being able to use it in a future build. SATA is going strong and has not end in sight so for the forseeable future you should be able to use it. SATA also uses smaller cables which improves airflow in your case and if you get a recent SATA drive-mobo combo then you might get NCQ which is a nice, albeit hardly essential, feature to have.