Thor - Much more versatile, equally as Strong but a bit less durable. However his ability to take damage makes up for that. Also has more skill and battle experience, to go along with being an excellent tactician.
Silver Surfer - Much more versatile, easily as strong and as durable. Also much faster, when it comes to flight speed.
Stardust - Unable to be physically harmed, more versatile.
Beta Ray Bill - Not as versatile as Thor, but his aggressive fighting style easily makes up for that. Also equally as durable, and as strong if not stronger.
Genis-Vell - Not much Genis can't do to Superman.
Hal/Kyle/Kilwog - Too much versatility, along with unbreakable wills.
Flash - Speed kills
Runner - Speed kills, add that to his cosmic abilities and Superman has no chance.
Fallen One- Potentially. Has been stated to have an infinite power source, and was stated in nova Corps files to be the most powerful of Galactus heralds.
Sentry - Potentially.
Morg - Look at Surfer
Fire lord - After great showings during Annihilation, I think it's safe to say that he trumps Supes.
Dr. Strange - Is an expert at using Supes primary weakness.
Dr. Fate - Look above.
Quasar - Much more versatile, easily manipulates energy.
Mangog - Basically can't be beat.
More to come...