Definitely .com, not just because it sounds all fancy and stuff, but it's the first thing people try when they don't know the address. Like, they hear about a games store called "Coolio Games" on the radio, but they really didn't catch it well, so they just give it a shot, and the first thing they try is "cooliogames.com"
And if instead you had bought "cooliogames.net", then you lost a potential customer.