Unreal (Epic) versus Quake (id)
Choosing sides: Neither Quake nor Unreal defined the first person shooter, but together they changed the genre forever. Both games prioritized online multiplayer above the single player experience, setting a precedent that can still be felt today. The influence of both can still be seen, too, as their graphics engines have been outsourced to dozens of other titles over the years. Which franchise you personally prefer, meanwhile, is simply decided by which one you suck at less.
Highlights: By the time the first Unreal hit shelves, Quake and Quake II had already had plenty of time to build a devout audience. When the two series made their historical moves into multiplayer-only territory, however, they were neck and neck. In fact, Quake III Arena and Unreal Tournament were released during the exact same week. PC frag addicts have been divided ever since.
The war between engines has continued to rage as well. Unreal's is currently showcased in mega hits like Gears of War and Rainbow Six Vegas, while Quake's is powering the Medal of Honor and Call of Duty games.
Outcome: Ironically, the next Quake game - Enemy Territory: Quake Wars - doesn't even use its own engine, but an adapted version of Doom 3's. And, based on interviews, the developers are more interested in competing with the team-based gameplay of Battlefield than anything from the upcoming Unreal Tournament 3. Is this the end of the rivalry? Will Unreal dominate over deathmatch unopposed? If id Software's demonstration of their latest and greatest tech engine last month is any indication, we doubt it...