I think if you layer them both- the cell shaded over the top as depth you'll the more serious, somber tone that you may be looking for. However you could easily grab one penal from the sepia tone on the left to make one part more impactful- that way you could choose which panel to highlight as the main idea of the moment in this scene.
Both work individually, but you would also combine them for depth. I kind of just like the sepia tone too, but I think that's because the way you shaded adds realism to the story.