Austin/Rock - No feud was ever close to generating that much revenue. They had 3 big time WM main events, WM 17 being arguably the greatest main event in history (imo its Rock/Hogan)
Austin/Vince - The creation of the Vince character saved WWF and literally single handily put whoever he feuded with on the map as a big time draw/star.
Sting/Hogan - Once again collectively this feud may have generated more revenue then any other feud ever beside Austin/Rock.
HBK/Hunter - Real tension that resulted in very long feud that produced tons of great matches, im still shocked they never had a big blowoff at a WM, wasted opportunity.
I honestly feel Austin/McMahon generated more revenue, seeing as how it lasted nearly 4 years, while Austin/Rock with both at their peak, collectively lasted no longer than 18 months and Sting/Hogan had over a years worth of build up but was pretty much dead by the summer of 1998.