My 2c. I pretty much agree with everything Sean said.
I haven't used the Reds yet as they are fairly new. But for sure stay away from the Greens. I mostly use the Blacks as that's the only way to still get the 7200rpm performance. If you do want the Reds, it appears my prices are way better than Memory Express currently so maybe give me a shout on a private email.
Personally, for large arrays I would use nothing but RAID6. For a 2 drive setup RAID1 is fine. I *always* go controllerless (software raid). You have so many more options for disaster recovery that way.
Seagate did put out a bunch of junk drives and I do return a lot. I live in hope they will clean up their act. All the latest DM series are NOT rated for 24/7 and they only have 1 year warranty. That said, they are the dirt cheapest 7200rpm drives around. 50% cheaper than 7200 rpm WD's. As they get cheaper, as long as the quality isn't too crappy, it may be cost effective to just let them die frequently and have some hot spares in the system for md to instantly rebuild to.
My current RAID6 16TB (2TB) setup is all Hitachis 7200's. They are often hard to find in Wpg/Canada. I haven't had a single drive failure yet (2 years so far). For performance, I couldn't ever imagine using less than 7200rpm. Performance is already a *little* less than I would have liked. And yes, it's just for data, no realtime or transaction type usage, but you can never have too much performance.
Also, when doing RAID1 I almost always do as Sean suggested and use 2 separate drive vendors. Usually a cheapo Seagate 7200 + a WD Black 7200. I've personally experience too many of the "bad batch" syndrome where you lose both drives before the 1st one comes back from RMA.