Amazon.com (AMZN 0.61%) is a great business, though the stock has significantly underperformed the Dow Jones year to date. Is every bit of upside already priced into the stock? In the following video, Fool contributor Daniel Sparks tells Fool.com's Erin Miller why he thinks Amazon's upside is limited. Plus, he points to an excellent alternative for investors: eBay (EBAY 2.20%).