With regards to performance, do remember that hard drives on ALL G5 powermacs only operate at sata1 (sata 150) speed. Most drives produced today are all sata 2, but the interface connections are the same. On some drives you can change the jumpers to downspeed them to sata 150, but in my experience it's not needed. The G5 will just work at sata 150.
My choice of drives for my G5s has usually been Western Digital (great performance and good value) or Seagate (a little more expensive but quiet). Both are reliable. I did have a bad experience with a Maxtor, but maybe I was just unlucky.