If it is a local company that has been around a while, and considering the very low prices they are offering you, sounds like either one would be fine. Both valves are excellent and both are easy and cheap to rebuild.
I would verify that it is greensand plus, I doubt greensand is even still available. http://www.clackcorp.com/downloads/i..._inversand.pdf
The valve warranty is from the manufacturer, if they are only a few months old, they would still have 4+ years warranty.