[lincpimp]

I prefer the 2 2s packs in series. Half the number of cells to balance and charge. Plus you can run them in series and charge them in series. This keeps the cells balanced at all times.

With a parallel setup you really want to charge the batts separately, or in series as 8s. Most chargers will not charge and balance 8s, you either need a pair of chargers than can be networked, or a hv charger and balancer combo, neither are cheap, and your options are limited. You can find 4s balancing chargers everywhere, and a series balancing harness is relatively easy to make.