2d or 3d for better perform on mobile devices?

I was wondering will creating 3d games perform better on mobile devices or will 2d? Which use less resources? I would think that 2d would perform better but not sure how mobile devices renders 2d games. Also will Cell-shading make games slower?

2d is easier to render.

Cell-shading make games slower because it use 2 time more polygon for the black outline