To help decide, a couple of questions.
1) will you do much dry camping?
2) how many days/year will you camp?
If the answer to (1) is seldom/never, and (2) is "a few weeks/year" IMHO a single or pair of 12V will do just fine and be the lowest cost solution.
If you dry camp a lot, then a pair of 6V has an advantage of more AH and the ability to withstand hundreds of discharges to less than 50% of capacity. Something 12V aren't real good at.
Also, if you intend to run a very heavy load (>100A) like inverters etc. for > a few minutes at at time, and do it fairly often then 12V offer an advantage in that they have lower internal resistance and are much better at high current draw situations.