The flooded lead acid heavy duty deep charge batteries will work the best and provide the most bang for your buck. AGM batteries can be used in non vented compartments and they can lay on their sides. That is there advantages, nothing more.
There are starter batteries, marine hybrid batteries, deep cycle, and heavy duty deep cycle batteries and the last type will provide the most current for a given amount of space.
Measure the available room and get the largest ones that will fit. My camper came with a group 27 battery but had enough room for a group 31 battery.
With a RV with room for 4 or more batteries there are advantages to breaking what would be a very heavy 12v battery into 2 lighter 6v batteries. With a camper with only 2 batteries this does not work as well as you need both batteries to be healthy is 6v ones or you have a problem. With two 12v batteries is one fails or a cell fails your camper's equipment still gets 12 volts.
When I added a second battery to my camper the available space meant that the second battery was going to have to lay on its side and so needed to be an AGM battery at nearly double the cost. Both needed to be the same for my solar charge controller so I ended up with two expensive AGM deep cycle batteries.
With an RV it is not unusual to have a discharge and only a partial recharge before discharging the batteries again. Flooded lead acid batteries are less likely to suffer damage from this than AGM batteries.