Hardwood gets my vote, since cork's not an option.
Granite, slate, and marble are attractive (++) and cold (--), as others have noted, and in a past life I might have voted for them. However, last year my wife's 96-year-old grandmother fell on her hardwood kitchen floor. She bounced, and suffered nothing more than a bruised hip. I shudder to think what might have happened on stone or tile.
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