I don't see how you can go wrong with either team. I like Sam's position on this.
But I think the answer is in Shocky's original post of this thread. There isn't a picture of Sting and Luger as a team. These were two guys who were thrown together singles wrestlers and had some success. I firmly believe that they were put together as a tag team expressly to advance singles storylines.
The Outsiders, on the other hand, formed a legitimate Tag Team force. Everybody knew them as former WWF Champ Diesel and former WWF IC Champ Razor Ramon. They had reps coming in to the team, just like Sting and Luger did. But The Outsiders managed to transcend the stereotype of former singles stars making a tag team. Their in-ring team work was flawless, and as a heel team they were classic. Whether it was invading WCW or whatever, for a while these two guys were the IT team.
Even in TNA, when Hall arrived one day for Impact, the sight of seeing Nash and Hall in the ring together was a REALLY neat experience. If Sting and Luger ever stood in the ring together, I venture to guess Mike Tenay would have to remind people they ever were a legit tag team. And even then, I wouldn't buy it.
Outsiders FTW.