Much is getting confused here. An Optima is a good battery and is an AGM. However, they do not have as much capacity per their cost nor their physical size as other AGM batteries. If you want an AGM for all the right reasons then that's fine, but I would look at others besides Optima.
Optima are designed to stand up to lots of abuse in racing, off roading, and activities like that. An RV battery really doesn't need to be built to withstand serious shock, vibration, being turned upside down, etc. So, it's a bit of a waste of money to buy one that is designed for that.
2 6v GC batteries are your best bet. This doesn't mean you can't have AGM, there are AGM golf cart batteries. If you want the advantages of AGM and the most amp hours in the space you have then AGM golf cart batteries are probably the way to go.
I would completely avoid gell batteries for RV usage. They are expensive and require very exacting charging for best performance. They also have less capacity per volume.