I've had the cobblestone tile for years and love it. Beginning a kitchen remodel now but definitely keeping the tile.

Slate needs to be sealed with a natural stone sealer. Depending on how you want it to shine will determine how often you reseal it. This is from my experience as we have slate on our entire downstairs floor. It's easy to clean with soap and water. We've had no problems with chipping. We washed and cleaned each piece of tile before we installed it. This helps eliminate tiles that may want to chip or crack. We used the dark grey grout and it looks really good.

I have had slate in my entry way for 20 years...damp mopping is all I have done...holds up well. Considering using it in my kitchen remodel next spring. Love the color variations.