If you're going to run it under the rug, get flat cable. They sell it and it's not ridiclous. I got mine at RatShack in the late 90's. There are no drawbacks that I noticed for the three years I did it that way. Don't bother otherwise. It'll look awful.
As for under the house, I doubt you'll have any problems. Any cable should suffice but make sure you seal any holes you drill. You don't need any creepy crawlies getting in your domicile.