Thank you, everyone :-).
Boy, is it hard to find specs for these rebranded batteries online. No luck so far, although I did like the suggestion of checking the specs!
The Interstate would be from a local supplier, and not an Interstate store. For some reason the interstate store said that they only group 65 they had was $300.
Since it sounds like they are roughly equivalent, I think I should go with the rebranded Deka, because I can get it from a big supplier chain, like O'Reilly or Batteries Plus, and that will be easier for warranty stuff on the road. (Another suggestion I very much appreciated).
As for why AGM, it's because I have brain problems. I have AGM house batteries, and my experience over the past few years of traveling is that if I have a wet cell for the chassis battery, I screw it up. I don't remember that they want different charging voltages, and have a different voltage when fully charged.
I do also have parasitic drains, and a tendency to park for extended periods of time. I try to keep things topped off with solar and plug-in chargers, but resilience is good.
3/4 timing in a DIY van conversion. Backroads, mountains, boondocking, sometimes big cities for a change of pace.