Factions like the Hydraxian Waterlords, the Zandalar, and the Argent Dawn all had their reputations firmly locked hand-in-hand with raiding. But reputations like the Shen'dralar, the Bloodsail ... they had no real purpose at all. When The Burning Crusade was introduced, the idea of factions was reworked. Suddenly you really wanted to gain reputation, because doing so meant you could unlock heroic dungeons or get neat incentives like armor, pets, and tabards.
Reputation design has changed drastically since then. Where once you got a tabard as a reward, now you slap one on and grind dungeons to earn reputation as quickly as you can. Different factions have different rewards, and rewards like shoulder and helm enchants are absolutely required if you want to perform optimally. So ... what was the best of the best?
What makes a "good" reputation grind? Is it the speed in which you gain reputation, or what you have to do in order to get it? I think this is an entirely subjective question, of course. Some people like speeding through content as quickly as possible.
Myself, I think my favorite reputation in the game from classic until now still has to be the Netherwing. Yes, it was a series of dailies, but the dailies were delightfully weird. And you could supplement those dailies with egg gathering. There was no limit as to how much reputation you could get in a day with the Netherwing; it was simply up to how many dailies you chose to do and how many eggs you chose to gather after that.
But more importantly, it was the way that the story of the Netherwing was presented. There was a reason to gain faction with the Netherwing, of course -- but at the same time, once you'd heard their sad story, you really wanted to help them out. You wanted to right what went wrong, and you wanted to be their hero.
And in the end, for all of the effort you put in, you got one free mount -- but it wasn't just a free mount. Before choosing the color of mount you wanted, you got to speak to each drake in turn, and all were so exceedingly grateful for everything you had done that they really wanted to continue hanging out with you. By the time you hit exalted, they loved you so much that they would do anything for you. It wasn't just an exchange of gold for something to ride around on -- it was a living, breathing, flying pal who utterly adored you.
That was so much better than simply hitting exalted with the Wyrmrest Accord and buying a random, faceless red drake that there is no comparison. With the Avengers of Hyjal, it felt like Blizzard was trying to get that experience back to a degree, but there was just something missing from the experience. The magic wasn't quite there.
I don't know if we'll ever see a return to the days of the Netherwing grind, but I hope that we do. The climb to exalted was so entertaining that ultimately, I barely noted the passing of days; I was far more concerned with what delightful little chunk of story I was going to get next. And in the end, the reputation reward meant far more to me than a head or shoulder enchant. With the many new factions available in Mists of Pandaria, I hope we see something similar. Let's face it -- I'd much rather see a cool chunk of story than slap on a tabard any day.