Having experienced much of the grunge madness first-hand in various Seattle/Ellensburg punk bands, my favorite top 5 "grunge" singers:

1) Mark Lanegan
2) Andrew Wood, Mother Love Bone
3) Mike Patton, Faith No More
4) Chris Cornell
5) Maynard, TOOL

Captured most feeling in vocals:
Hands down Mark Lanegan, if you love the blues almost all of his solo albums are brilliant, and the last two Screaming Trees albums (Sweet Oblivion and Dust) are WAY underrated. And not a bad QB for Ellensburg High School.

Best Range:
Mike Patton, or Chris Cornell to close to call

Personal Favorites:
The absolute Godfather of Grunge, no not Kurt Cobain or Neil Young, but Mark Arm from Mudhoney. If it were not for "Touch Me I'm Sick", there'd be no SubPop, no garage rock revival in Seattle, and thus no grunge. Arm is the only singer crass enough to dedicate the song "She's Drinking for Two" to his pregnant wife!

Most Wasted Potential:
A four way tie between Cobain, Wood, Layne Staley, and Shannon Hoon (before anyone piles on, no not really "grunge")