As far as battery brands go, I think you can do much better than Optima for an AGM battery. I think Odessey, Deka, or Lifeline all are likely to give you better reliability.
I don't know what sort of space constraints you are working with, but if at all possible I recommend using a single larger battery vs. two smaller batteries in parallel. Two batteries in parallel will often not yield the capacity gain you are expecting on paper because of the way the two batteries will interact with each other. I ran a dual battery setup in my Bigfoot for many years, and we never really had 2X the capacity of a single battery. I've since converted to a single Lifeline 4D size battery and are very happy with the performance of that setup.
I've done the same thing in my Horizon trailer which originally came with 2 Group 31 Dekas. I managed to squeeze a single 4D battery in the nose box and I have much better capacity performance with a small weight savings to boot.
If you do decide to go the dual battery route be sure to get identical batteries with the same manufacturing date code. This will minimize the issues associated with running two batteries in parallel, but in my experience not eliminate them.