How strong is Superman?

Superman is generally written under the assumption he can lift in excess of 100 Quintillion Tons.

Often Superman can lift double that, with one hand, effortlessly.

(According to Batman, a Kryptonian has enough strength to shatter the Earth with a single punch.)

On a couple of occasions he's been shown lifting "half the weight of eternity" or moving "dozens of planets across the universe." even holding a micro Black Hole in his bare hands.

To squeeze coal into a diamond you need over a million tons of pressure to force the carbon atoms to align into the most rigid structure on earth. Superman does that with just one hand! So as for strength he is really impossibly strong. If Superman and the Silver Surfer REALLY had it out strength wise, the solar system would not be able to contain them. And as far the Hulk, Superman hands down.

Superman's strength level varies based directly on the amount of yellow sunlight he's been exposed to. He has been shown to vastly augment his powers by flying into the Sun. (Sun-dip)