"I think he's proved himself now as both a director and an actor, but I will say he's best in the movies he directs," Franco, a veteran of Sam Raimi's Spider-Man franchise, said at the Toronto International Film Festival while promoting Palo Alto and Child of God.
"Maybe he should direct it," he said. "I think he should direct it."
Franco also doesn't think that Affleck deserves all the hate he's getting for his first superhero role.
"Daredevil wasn't my favorite movie, but I don't blame Ben for that," he said. "As an actor, there's this crazy thing where you could be good, you do good work, but then if you're in a movie that's not so good, they blame you…That's just crazy thinking."
The Comic-Con contingent practically imploded when Warner Brothers announced on Aug. 22 that Affleck had signed on to play the Caped Crusader in director Zach Snyder's follow-up to his first Superman flick. Henry Cavill will return as Superman.
"I think he'll be a good Batman," Franco said.