I'd have to go with JLA for sheer power alone.
As for Superman vs the Hulk...?
I once read a Marvel/DC crossover that was written by Jim Shooter, who was at that time Marvel's Editor in Chief. Of course, this was before Shooter was shit-canned for his Secret Wars II flop and replaced by Tom DeFalco.
There was a brief scene in this crossover in which the Hulk was on a rampage, reeking havoc in Metropolis. It was unclear as to what he was so pissed about. Superman intervenes and confronts the Hulk. Superman stands there in his Superman stance. Feet apart. Fists on his hips. Elbows akimbo. Cape waving majestically behind him, while the Hulk is jack-hammering Superman's torso with his fists, with little to no effect.
This of course, infuriates the Hulk even further, and as we all know, the Hulks strength increases dramatically as his anger escalates, and so the outcome is in doubt.
But even through the thundering din of the Hulk's fists crashing into Superman's upper body, the Kryptonian's super hearing detects something....a high pitched screeching sound emanating from what appeared to be a mechanical insect drone hovering about the Hulk. Clark deduced this was the very thing that was driving the Hulk's rage, so he immediately vaporized it with his heat vision. Later he finds out that this was all an elaborate plan perpetrated by Dr. Doom to test Superman's powers.
The Hulk begins to calm down with Superman's help and then he decides to bolt with those flying leaps of his, probably back to Gamma Base in the southwest. Ultimately, Supes teams up with Spider-Man to fight Dr. Doom and the Parasite.
It was kind of cool to see the melding of the DC Universe and the Marvel Universe.