As specified in the links, only the first PC is suited gaming. That's because it has a reasonably good graphics card installed (ie The HD 6870), which is essential for gaming. The second PC has a cheapo discrete graphics card, which isn't much use for recent games, and the third PC only comes with integrated graphics (forget it!).
Summary:- The Medion is the only one that's any use to you (without customising the PC).