I have an "early 2008" Mac Pro with a Pioneer DVR-127D that makes a pretty horrible noise and no longer read or write.
What is the best unit to replace it with?
^^^^Actually, that's not quite true. The 2008 (3,1) Mac pro Optical Drive interface is Ultra ATA/100 not SATA as in later Mac Pros. I don't think you can find a DVD with that interface today. You may need something like this:
http://www.amazon.com/PATA-SATA-Serial-Converter-Adapter/dp/B001MW926I
Also, my recent experiences with Pioneer Optical Drives have been very poor.
Lou
I should mention that the early 2008 MacPro has unused SATA ports on the logic board. It's not a difficult task to change out the ATA optical drive to an SATA model. No ATA to SATA converter needed.