Well...greatest protest singer of the 60's, eh?
For sheer personal dedication and idealism: Joan Baez
For lyrical and overall impact and depth of theme: Dylan
For singlemindedness: Phil Ochs (though I find him hard to listen to for some reason, probably because he's too literal for me...too singleminded)
For Native American themes and fiery intensity: Buffy Sainte-Marie
"The Universal Soldier" by Buffy is possibly the most effective antiwar song ever, for presenting a simple philosophical truth in a beatifully effective way.
The most subversive protest material was always Dylan's, because he protested on EVERY level, not just on the obvious ones. "Highway 61 Revisted" is protest all the way through, for instance, but it's not literal protest in the usual sense...it protests not just war or segregation, but everything.