Assuming you have enough charger power to charge at a full 1C rate, there is no diff in balancing a 2S or a 4S, so its not a matter of one being easier than the other, its basically the same process whether its 2cells, 4 cells or 6.

Wiring in series cause the voltage to add, so two 2S lipos in series becomes a 4S equivalent with same capacity. The C rating does not change. If we start with 2S 5000mah 30C lipos, in series we have a 4S 5000mah 30C equiv. The discharge current (5000/1000 x 30) remains at 150amps.

In parallel, the voltage stays same, but capacity adds. The C rating is unchanged. So this pr of 2S wired in series would become a 2S 10,000mah 30C lipo equivalent. Discharge amps would change because the capacity changed, not the C Rating - 10000/1000 x 30 = 300amps. It doubled because we doubled the capacity, the C rating did not change.

The combos you propose would both have 160amps discharge, they would be no diff electrically as far as disch amp are concerned. Physically, its easier to run two 2S in series since they're much smaller and much lighter. The diff is in the run time, the 8000mah from the paralleled combo will generate roughly 2x the run time. The decision for me would be is the extra run time worth the extra weight and does the RC physically have the room to accomodate the size of two 4S pacs. You'd also need to adj suspension as well to deal with the extra weight. I would be running in series.