Superman's costume is the most recognizable superhero costume in the world, yet it is also one of the hardest to pull off in live-action. Aside from needing the suit to be not silly in live-action (it's Superman), It also needs to have the basic design of being tight-fitting and have primary colors of blue, red, and yellow. It needs to make the person wearing it look like a strong man, larger-than-life, yet approachable to the crowd - friendly and welcoming.
This is why any changes that make it vaguely military or armored does not work - it makes Clark look unapproachable and intimidating when he is supposed to be a charismatic friendly face.
We have had so many live-action suits throughout the years, and it proves just hard it is to crack the winning formula for it. Then again, we still did have some good ones throughout the years, didn't we? Maybe one day through trial and error, we will finally see the perfect suit. Or maybe the perfect one already happened, sitting comfortably still at number 1.
13. Kirk Alyn Suit
In last place by default is the costume worn by Kirk Alyn. We are still not in the era wear the costume designing techniques are refined enough for us to have a proper suit for The Man of Tomorrow. As a result, we have clothing that looks like it can be made by anyone with a sewing machine.
Look closely enough, and we can see that the upper part of the costume is just a sweater attached to a Superman emblem and a cape. It is not form-fitting enough to fully emphasize Kirk Alyn's physique, nor would the censors of the time would even allow for such an overt pronunciation of muscle.
It is unfortunately a product of its time. A suit that was enough for anyone watching in the early days of TV, but years of costume refinement in film and TV have shown us we can have better. Maybe the people making this wanted to make this most comic-accurate as it can be, but the limitations of the time made it impossible. Sometimes Clark wears pajamas to fight crime.