Superman Superman has no upper limit to his powers, whereas Shazam does.
Superman becomes supercharged when he bathes in solar energy for a while. In the Justice League Sixth Dimension storyline, he flew through like a dozen suns that were arranged into a flight path by Batman, and as a result he became so strong he was able to one-shot the World Forger, one of the most powerful beings in the multiverse.
In the New 52, there was a Kryptonian villain, H'El, who had a wide array of remarkable powers (all of Superman's powers, plus telekinesis, telepathy, matter control, teleportation, and a bunch of other things) that he gained because of prolonged exposure to different suns (yellow, blue, and other except for red). Superman should be able to gain the same powers by bathing in different colored solar energy.
Much more simply, Superman can get supercharged just by flying into the space, diving into the Sun, and soaking in there for a few minutes. The longer he soaks, the more powerful he'll become. In the Justice League One Million storyline, Superman basically became a god by living inside of the Sun for over 85,000 years.
As far as I'm aware, Shazam doesn't have an easy way to get supercharged.
Now, in a fight, Shazam has an advantage because he's inherently magical, and Superman has a lethal susceptibility to magic. Shazam has knocked Superman unconscious before. But your question isn't "Who can win in a fight?", it's "Is Shazam stronger or weaker?" My answer to that is Superman is stronger because he has an easy way to become more powerful.
Superman becomes supercharged when he bathes in solar energy for a while. In the Justice League Sixth Dimension storyline, he flew through like a dozen suns that were arranged into a flight path by Batman, and as a result he became so strong he was able to one-shot the World Forger, one of the most powerful beings in the multiverse.
In the New 52, there was a Kryptonian villain, H'El, who had a wide array of remarkable powers (all of Superman's powers, plus telekinesis, telepathy, matter control, teleportation, and a bunch of other things) that he gained because of prolonged exposure to different suns (yellow, blue, and other except for red). Superman should be able to gain the same powers by bathing in different colored solar energy.
Much more simply, Superman can get supercharged just by flying into the space, diving into the Sun, and soaking in there for a few minutes. The longer he soaks, the more powerful he'll become. In the Justice League One Million storyline, Superman basically became a god by living inside of the Sun for over 85,000 years.
As far as I'm aware, Shazam doesn't have an easy way to get supercharged.
Now, in a fight, Shazam has an advantage because he's inherently magical, and Superman has a lethal susceptibility to magic. Shazam has knocked Superman unconscious before. But your question isn't "Who can win in a fight?", it's "Is Shazam stronger or weaker?" My answer to that is Superman is stronger because he has an easy way to become more powerful.