Well, then, how about saves divided by save opportunities? What could be a fairer metric than that? That puts this completely in context. Sure, Rivera had more save opportunities; he played for a better team. But I think we can admit that both pitchers had long careers, and that they were one of the best closers in their league year in year out for almost exactly the same amount of time. (Interesting that Rivera only led the league in saves three times.)
On save percentage, they are 2 saves from being identical over the course of 18/19 year careers.
Wanna talk WAR? Then lets do so. Rivera's WAR is 77th among pitchers and 227th all time. Why on earth would that qualify you for being the first unanimous HOF selectee? It kind of makes him marginal for even being selected at all! Why? Because WAR is a stupid index for closers. They don't play enough innings to get a decent WAR.
Why not stick with looking at what closers are supposed to do? Close. If you do so, Rivera and Hoffman are incredibly similar, with the notable exception of post season. For the umpteenth time, Rivera is the best ever closer, no question. But Hoffman was a close second.