It is much more complex than simply what it on the price tag. It starts with your camping habits & how many AHs you can get into the battery space.
A solution seldom suggested is using a single 4D case sized battery. A 4D battery is about the same size as 2 GC6Vs & similar AHs. I imagine the weight is about the same as 2 6Vs. The small advantage is simplicity of cabling. No in series linking of cable to be monitored.
What is the service life of a 4D vs 2 6V GCs? I don't know. I use a 4D, but it is an AGM. Being an AGM opens a whole nuther can of discussion worms but my last AGM 4D gave me 9 very active years.