Hi,
The real answer is "it depends".
If you are like me and use your inverter LOTS then 12 volt jars may be better.
If you go AGM because of low maintenance be aware that charge protocols need to be followed "to the letter". There is essentially no difference between 6 and 12 volt jars in agm chemistries, but the 12 volt will double the number of cells and may be better for heavy inverter use. You could do a lot worse than two 12 volt 8D agm's.
If you boondock and have some solar the batteries will last a lot longer. My banks are 5 and 9 years old now and still meet my needs.
If you have deep pockets, then consider LI technology. It saves on weight but again--you need deep pockets.
So, examine your camping style and then pick a battery type.
