Ava would have had amazing chemistry with;
John Payne
Dick Powell
Richard Widmark
Robert Ryan
Dean Martin
Victor Mature

Are the two actors I wish had been among AG's leading men! They both were the male versions of Gardner; dark exotic/ethnic looks, smoldering, volatile, loads of animal magnetism. I'm sure they would have burned up the screen with her!
I don't know how reliable it is as it's in a book by Darwin Porter who I've heard is quite sketchy, but according to his bio of Brando, he and AG were approached to play the gypsy leads in a film called "No Return". If that indeed was true, what a pity it never transpired!

I think Ava Gardner and Arthur Kennedy would have made an interesting pair especially in a Film Noir, a genre that Ava should have appeared in more often.

I think John Garfield would have been another choice for leading men for Ava.

Oh okay. I love Jeff Chandler and Montgomery Clift. I don't know who the other guy is.

Ava and Paul Newman both appeared in THE LIFE AND TIMES OF JUDGE ROY BEAN, but shred no scenes. Ava and Anthony Perkins both appeared in ON THE BEACH. But the rest of that list are fine; Ava and Frank Sinatra would have been interesting.
I'll also add
Jeff Chandler
Robert Stack
Montgomery Clift

I have not seen all her movies. Sorry if I pick someone she has been with.
Paul Newman
Anthony Perkins
Marlon Brando
Jimmy Stewart
Frank Sinatra
I know you wanted leading men but I would have really liked to see her and Gloria Grahmn in a movie together.

I was also thinking Frank Sinatra. Imagine the fireworks off-screen and on.
I was also thinking;
Robert Preston
Cornel Wilde
Rock Hudson
Rod Taylor

I also agree with the William Holden selection.

It sounds cliche, but I would've liked to see her do a movie with Frank. Also, Marlon Brando, Jimmy Stewart and Henry Fonda. I like the idea of her and William Holden working together as well!
"I got you some cigarettes - you buy yourself something pretty."