I am going to redo this. I originally had The Defenders winning but it was a quick write-up that never felt quite right. I'm going to have to go through this match-up a little more carefully.
My gut tells me Justice League wins this but... like Flash being an x-factor, I consider Silver Surfer to be more of an x-factor (but Superman counters him for a while).
The fight is... Marvel's Classic Defenders:
Dr. Strange, Namor, Silver Surfer and Hulk ... vs
Classic Justice League
Superman, Batman, Wonder Woman, Flash, Green Lantern, Aquaman and Martian Manhunter
By classic... I have to go back to their power levels in the mid-1970s period (around the time The core Defenders were active).