Which kickboard is better for kitchen & pantry

It's purely a matter of aesthetics.
The brushed metal kickboard look was popular some time ago but the majority of people now just go with a matching colour kickboard to the rest of their cabinets.
The aluminium and stainless are no more water proof than a standard colour kickboard, so unless you particularly want those finishes there is no real benefit other than the fact that they hide dirt and marks better.
I have matte white kickboards and have never had issues with them getting dirty. It's a good practice to give your kickboards a wipe down every now and again

The stainless or aluminium are both just veneers of the product stuck on moisture resistant particle board. It's not solid material, so it's no different to a melamine or similar.
What is more important is that the kickboards are sealed to the floor to prevent moisture and dirt getting in under the kickboards.