Having seen all the Mad Max films except Furiosa, I'd actually consider all of them to be excellent.
The first is clearly a very low budget endeavour, but it has a scrappy underdog charm that I really quite like.
The second is the best thanks to its top notch action.
The third slows down a bit to invest more in worldbuilding, and while the action isn't quite on the same level as Mad Max 2, it's still very enjoyable.
Fury Road is a visual feast with, for my money, some of the coolest action scenes ever committed to film and masterful pacing.
It's one of those rare franchises to me that doesn't have a weak entry.