Your Converter / Charger is the limiting factor when it comes to battery selection..... as well a budget. Lithium Batteries would require you to replace your Converter / Charger with one designed to charge Lithium Batteries.
You stock WFCO Converter can handle flooded or AGM batteries but it won't support GEL (a variant of AGM).
AGM's are maintenance free so as long as they are charged properly, they are a good choice if you have the money. But I would not replace the stock batteries until they were showing signs of needing replacement..... unless you can use them for another application.
__________________
|