Old McKenzie Pass before you get to McKenzie Bridge and the junction to Highway 126.
This waterfall puts out a lot of mist. If you're going to get down into the creek and shoot, expect to lose many of your shots to water spots no matter how much lens wiping you do. It's a good idea to bring a raincoat for your lens and camera, as well as waders for yourself.
Proxy Falls is definitely a calendar pinup of a waterscape. You'll want to go in late spring or early summer, when the flow is at its highest. The observation area above the creek offers uninspiring perspectives of this magnificent waterfall. You'll want to get down into the creek to get your best image. You will have to get dirty crawling under fallen logs, but it's worth it.