In terms of an on going angle or storyline I'd give it to Bret Hart and Steve Austin. Austin's incessant interference in Hart's big matches and costing him both the Royal Rumble and the WWF title added so much fuel to the fire though Austin was definitely more popular than Hart months before the 'Mania match and you could argue the heel/face switch occurred months before the WWF actually acknowledged it.
Second would be the first Michaels/Taker feud. Michaels was fantastic playing it dirty and taking cheap shots and generally running awway from the Undertaker anytime the deadman got the upper hand. That psychology of that first Cell match hasn't been repeated since - save perhaps for the one with Edge.
On matches alone I might have to choose Angle/Benoit - did these guys ever have a stinker? Their 2001 series was sublime.
Austin and Rock may have had some classic encounters over the years, but I have to go with Undertaker and Shawn Michaels. Absolutely amazing chemistry, awesome presence between them and they still have the ability to tear the roof off of any building they walk into.
Austin and Rock: Only them two could headline 3 manias and entertain the crowd the way they did. Wrestlemania X-7 is still my favorite main event in Mania history just good stuff. Austin and Rock had great chemistry whenever they stepped into the ring together
Tiger Mask And Dynamite Kid: I recently watched the famed Tiger Mask and Dynamite Kid matches from the 80s and HOLY SHIT this is some awsome shit. Easily some of the best wrestling from the 80s and so inovative to what will follow in North America with the ECW promotion in the mid 90s
You should include Steve Austin vs Triple H in there actually. Their No Mercy '99 match was great as was the 3 Stages of Hell of course while the Survivor Series 2000 match was very good safe for the awful ending. Trips and Austin allegedly worked classic matches every night in the house shows in early 98 while Michaels was out with his back - it was Triple H on his DVD I think that said this.