@Riot: why are Quinn and Talon rivals?

Their headwear looks similar and Talon wasn't going to have any of that.

I think that It really just boils down to how they are characters in regards to where they stand. A sneaky assassin from Noxus and a scout from Demacia are bound to have some difficulties, and if I'm not mistaken they were made relatively close to each other. I don't think there's any hidden theory, just that they needed a rival, and so they got one.

One tries to assassinate high priority targets and the other specializes in chasing and finding stealthy opponents.

As i recall, Talon is Quinn's twin brother who she thought had died from falling of a cliff. Talon(Caleb) probably lived and found himself in Noxus without knowing his real name. Also, I remembered Quinn was tracking down an assassin but never brought him to Justice. Perhaps she recognized him and kind of stalking him now while he and Katarina are tracking a general.

Let them both become a couple. Quinn marrying talon will be interesting. I wonder what Quinn will think of talon assassinating people after they become a couple.

Actually, being the lore lover I am (plz rito) the Quinn teaser was actually a journal or Quinn hunting down Talon, as he attempted the life of KING JARVAN THE THIRD.

You can view it Here: http://leagueoflegends.wikia.com/wiki/Quinn/Background