An interesting thread is over at the whirlpool.net.au forum dealing with the question of which drives to go for if you are building or setting up a NAS. The original poster asks whether the Red or Green drives should be used if setting up a NAS that will not be configured using RAID for data redundancy.
Different views are expressed, but I agree with the post recommending the Red drives:
...The reds have a longer MTBF, longer warranty, more support for hardware RAID controllers, they are faster than greens and have different firmware which has fixed many of the compatibility issues greens had with NAS units. It is very clear why they cost more and in your case I'd recommend the red drives.
Even if you aren't planning on using RAID now, buying the Red RAID drives makes sense to me to future-proof your purchase.