There have been times when the winner of a competition between these two would have been a no-brainer: eBay (NASDAQ: EBAY) was the unquestioned king in online reselling, while Overstock.com (NASDAQ: OSTK) was perennially floundering. But times have changed: After it spun off PayPal, eBay lost its major growth hook — and Overstock now trades for just a fraction of its total sales.