We have very hard stone tiles. We're not even sure what kind of stone, just something that makes our heels and calf muscles ache when we've been standing for hours at the stove and countertop. Unfortunately, we didn't get to choose them.
Our pick would be hardwood floors. We like the way they make the kitchen seem like any other part of the house; it should feel like a living room, given how much time we spend there. We also think they're pretty easy to clean (unlike our mottled stone, which seems to pick up stains in odd places).
You can check out various kitchen floors in our Kitchen Tours archive.
(Images: Peter Murdock/Metropolitan Home; John Reed Forsman/Metropolitan Home))