1) books, models , video games.
2)Dark Angles/Space Wolfs
3)Imperial Fists/Iron Warriors

1) stuff
2) Imperial Guard/Space Marines; Orks/Grots; Word Bearers/Black Legion
3) Squats/Tyranids

1) Books & Audios, I mainly buy the rulebooks for lore now. Though I've started my 30K themed Imperial Fist force recently. Heavily into digital Warhammer gaming
2) No contest for me: Imperial Fists vs Iron Warriors.
3)Imperial Fists vs Iron Warriors...make it so Ivan.

3) Valrak vs Ivan.

3) Valrak vs. Spam Bots

What's the difference?

1) Warhammer 40,000: Rogue Trader (1st edition rules not the role-playing) all editions, all games, been waiting for EC a longe time.

2) as a Space wolves player there is only one real rivalry Space Wolves vs Dark Angels.

3) Wouldn't mind lecturing some Dark angels player how to properly capture a strategic point or how to kill heretics, Xenos and traitors alike.

1)Video games(starting with the first Dawn of War), once upon a time Tabletop but no more today(just dont ask why) and the countless hours ive enjoyingly spent in lexicanum, forum and codices exploring the deep universe behind the game.
2)That major incident where Space Wolves take up arms against the Inquisition and their Grey Knights. If the question wanted between persons comes to my mind Yarrick and Ghazghkull.
3)Inhouse Chaos rivalries Khornate vs Tzeentchi or vs Slaaneshi id definitely like to see at launch.

The difference is Spam Bots can't block the Imperial Fists for making it into the game! *Zing*