I always mentally group Faye Dunaway with Jane Fonda; after Julie Christie (and before/along with the emergence of Diane Keaton and Meryl Strep), they were the premier American actresses of the late 60s/early 70s. They held it down for the women.
It's funny that Dunaway auditioned for this role; I do know that Fonda was one of several actresses considered for Faye's titular role in Bonnie and Clyde. They also did their pair of "political thrillers", with Klute and Three Days of the Condor, respectively. I could see Dunaway filling in for Fonda in They Shoot Horses, Don't They?, even if the result would be of a slightly lesser caliber.
When it comes to who's superior, that's a toss-up; Fonda has a much higher number of good to great performances in more noteworthy films. However, Dunaway's film highs arguably eclipse Fonda's; nothing Fonda has done is as landmark as Bonnie and Clyde, Chinatown, and Network. Fonda = quantity, Dunaway = quality. However, I think Faye lacks Jane's dramatic chops; ability/performance-wise, Fonda takes it.
Fonda was prettier, despite being older; Dunaway seemed to age awfully fast. However, for my money, Dunaway in Bonnie and Clyde is perhaps the sexiest performance ever by a female. She is red hot in that movie. Even the most challenged male would find his impotence cured by a simple caress.
It would have been something to see them play against one another in their prime.
"...if that was off, I'd be whoopin' your ass up and down this street." ~ an irate Tarantino
'I think Faye lacks Jane's dramatic chops; ability/performance-wise, Fonda takes it. ' ------------- Never got that. Faye has more intensity; Fonda is overrated and became more noteworthy due to her leading lady looks