Personally, I don't see the any advantage of AGM batteries that can justify the extra expense. Yeh, there may be some benefit that will, in some limited circumstance, have a return but IMHO they are limited.
The AGM will work in any position so if your MH happens to be on it's side or roof, you will still have power.
A well maintained flooded cell with last just as long as an AGM (I got 9 years from the interstates) and with modern inverter/chargers water addition is pretty much a think of the past.
I just install a battery watering system that eliminates opening the caps and also recombined the gasses. End result, no mess, no corrosion, and adding water is a 1 minute operation.
Since most of the AGM toted advantages are more marketing hype than reality....I'll stick to the flooded cell.