Other than hearsay, there's nothing to distinguish these drives in terms of reliability. It will be easier to keep the lower-speed drives cool, so that might help.
Here's some hearsay: I've been using WD Green drives for quite a while now, including two 2GB drives I purchased about three months ago, and have been quite happy with them. I use them as bare drives in a USB drive dock, so cooling isn't an issue for me. They get handled a lot more than an internally mounted drive would, but that hasn't caused any problems so far.