Neutral wiring in a panel
In a main service panel; where the grounded (neutral) is bonded, you can land the grounded (neutral) conductor at either bus bar.

In a panel where the grounded (neutral) and grounding bus bars are separate, you can only land a grounded (neutral) conductor on the grounded (neutral) bus bar.  In this case, you'll either have to install a grounded (neutral) bar on each side of the panel, or route all the grounded (neutral) conductors to the same bar.