Zack Snyder boasted that he saw 1,500 incarnations of Superman's costume before selecting one for Man of Steel. Concept artist Warren Manser has shared some of his Man of Steel concept art, including Superman in the red briefs.
In an interview with Film Sketchr, Manser says that Snyder did indeed see a lot of iterations of the costume:
I recall hearing the term 'due diligence' in reference to the Superman suit and specifically to the red briefs. It was extremely important that we created a costume that would respect the Man of Steel's origins while taking him to a new level. I don't even want to venture a guess at the number of variations, but he may not be too far off. I had so many photoshop layers that I lost count.
Unfortunately, I cannot recall a timeframe, but when our director was satisfied that we exhausted all plausible avenues, he made the call. We said goodbye to the red briefs!
You can see more of Manser's concept art, with plenty more Supermen, from the film on his site.