Deep cycle battery: RC vs Ahr??

I don't really have a particular battery (or batteries) picked out. I've worked with a couple of local automotive electrical repair shops and they say RC is the way to go. And Interstate says on their website that RC is a better way to state the "capacity" (for lack of better terms). Both places really know there stuff when it comes to cars and trucks and generators, etc but not necessarily with the use of lead acid batt's in RV's like people on this forum do. That's why I asked.

I suppose, if push came to shove ... I'd be leaning towards the Duracell Ultra High Capacity Battery for Deep Cycle 6V RV (SLIGC115) from Batteries +. I can pick up a couple of those for under $100 each.