I'm not a seasoned vet just yet, but well on my way as a wannabe... that said, I'm running a pair of RayOVac SLIGC125s currently, 6V/235Ah, nominal 12V. They've been good to me, this will be their third winter and they're still enduring, bought them as a set, new.
There are mixed stories about used batteries out there... personally that's the one component of the system I avoid used like the plague... it's difficult to near impossible to determine the remaining health without putting them thru their paces a couple times and seeing how they react.
Just my take on it, from learning the hard way on earlier smaller systems. Some report fantastic success, I'm not one of them.
As Oztules pointed out, new or used is an easy kill for the first go round... even as forgiving as flooded is, it still has it's limits. That said, I agree with the sentiment of at least using flooded. Sealed cells (AGM/SLA) are much less tolerant of abuse.
For what that's worth