Two considerations.
Total Resistance of each battery circuit should be kept low (low voltage drop = no unwanted heat) by properly choosing and sizing cable, lugs and quality copper bus bars.
The resistance of each individual battery circuit should be the same for each battery pack so they charge and discharge at the same rate. In other words it doesn't matter if the black wire is longer than the red wire as long as its the same for both packs as you have shown in the drawing.