Is there any advantage to using multiple tracks in this PCB design?
I'd turn the GND into a fill.
The difference in performance between your two designs is rather small, but you can get a lot better than both of them by making the traces wider. Filling the entire plane except for the space taken by the other traces is an extreme of that.
If you have this manufactured rather than etching it yourself, there is no reason not to go double-sided, as your design will be produced together with a lot of other double-sided designs on the same large PCB, in that case I'd turn the entire backside into a GND plane, and make two smaller zones on the front for +5V and +12V.
Having two planes gives return currents a nearby path with good coupling, so this is the best solution from an EMI perspective.