Hardwood, hands down.
Carpet, once laid, starts to deteriorate -the sisal backing is a natural fiber and it creates dust. There is no way to 'clean' a carpet without removing it and washing it in a vat big enough. All the 'cleaning' done is nothing but surface dusting, with all the sand, dead skin, bug parts and germs resting comfortably within the weave where no cleaning can get anywhere near it. With wear, it puffs back up to the top, period. Even optical brighteners can't make a carpet look clean for long.
They provide ideal conditions for bedbugs, dust mites, carpet beetles (obviously) and all kinds of other wildlife and pathogens, without mentioning the chemical stew offgassing into the house, and holding onto odours of all kinds.
Slippers and socks will keep feet just as warm without giving odours somewhere happy to live.
at 6:12 PM on Jan. 21, 2011