TSK! Someones left beer cans on your sidepod!
From a cooling standpoint, it depends on how effective the radiators are.
Parallel = potential for more cooling capacity as you are effectively flowing more coolant to the radiators. More complicated as you have to split the plumbing. Series = better cooling on lower flow rates, probably eaaiser to plumb in.
Your best bet is to estiamte the cooling capacity of the radiator, then calcualte the maximum fluid flow rate with each scenario. Which ever gives a higher heat transfer value is the one to go for. This will also depend on how good the pump is.
I'd be tempted to say that parallel will probably be better.
I don't see the point in the splitter in the red case, unless the flow was seperating on entry and stalling a bit in the sidepod or something like that.