Coke or Pepsi. Blond or brunette. Batman or Superman. For every great thing in this world, there's at least one other that stands in its way, forever dividing a group of people who would otherwise love the exact same stuff.
Videogames are not exempt from this behavior. Even before the internet let everyone tell everyone else that everything they like is retarded, people would get in each other's faces about which series they liked more. These seven cases cover the biggest and most divisive franchise confrontations the industry has ever known.
Silent Hill (Konami) versus Resident Evil (Capcom)
Unreal (Epic) versus Quake (id)
Street Fighter (Capcom) versus Mortal Kombat (Midway)
ESPN NFL 2K (Visual Concepts / 2K) versus Madden NFL (EA)
Virtua Fighter (Sega) versus Tekken (Namco)
Final Fantasy (Sony) versus Final Fantasy (Nintendo)
Super Mario Bros. (Nintendo) versus Sonic the Hedgehog (Sega)