This is going to be presonnal, I like Seagate disks, we use around 30+ Terra bytes worth in 18GB chunks organised into 3 SANs, we get very low failure rates, i.e just a handfull per year at most.
I have 3 Seagates in the G4 at home, mirrored 10 GB ATA root disks and 1 * 200 GB SATA for VIDEO. All solid as a rock. I also have, in the same machine, a COMPAQ 40GB Ultra SCSI III disk for AUDIO, also solid as a rock.
However I go to another place of work (self employed) and I get riddicule for using SEAGATEs, although I think they mst be older and well used disks.
The only disks that have failed in my Macs so far have been IBM, the ones that were in the Mac originally, i.e. both ATA ansd SCSI. Having said that they have taken a lot of hammer.
Go for as much as you can get but you may consider used ones, since its "scratch space" and by that I mean temporary working files used by PhotoShop and the SAVED output is on your 250GB disk, it may not be that important to have a really expensive disk.