A lot really depends on how you use your coach batteries. You mentioned needing to rely on your rig year round, but are you generally on shore power or a genny and just need to keep the power up while traveling, or do you need to rely on battery power for extended periods of time?
What things are you wanting to power off your batteries, for how long, and how critical is it that they stay powered up? ie., in your efforts will you have medications or such in the fridge that need to be kept at temperature? Things like that.
Edit: Along with what Bruce said... you also want to purchase the most recent production date you can find and both batteries should have the same dates.