Technically, the Humble Frozen Synapse bundle. I wanted to get a few people to do the FS multiplayer, so I spent $20 for one bundle, then something like a cent for another copy for myself. The copy I gave away was technically not MY copy, so technically it was a cent. I played FS for maybe 7 hours.
The Orange Box I pre-ordered. Which was awesome. But it probably wasn't a full 4,000 times as awesome. Minecraft gave me a few hundred hours at only 15 bucks, but it's still firmly at over a cent per hour. Civ 5 I'm at around 300 hours but still, I paid full price.
If we arn't being cheap though, Id have to give the prize to one of those 3. Of course, this is barring FtP games.