Whether one is stronger or weaker is not really the question; if you stop to think about it, Ganondorf and, the antecedent to nearly all of the current Zelda foes, Demise are almost identical in power. The tools that Link garners so that he may defeat them don't differ except in one or two factors, at most. But how does that gauge which is the mightier? Well, in my belief it's important to analyze the similarities over the differences.
Beware of some SS plot spoilers beyond here.
As most of us may already know, Ganondorf is capable of great feats thanks to the Triforce of Power being in his possession. He can levitate himself, generate electrical orbs, summon spiritual riders, possess princesses...and even turn into a giant beast, sometimes boasting twin daggers. This suggests that he is a foreboding combatant that any sane or fearful man would turn tail and flee from. During one point, Ganon was able to take over an entire kingdom and rule it for a seven year period. How he achieved this, as far as I know, is unverified. But the point stands that with his power he
could make Hyrule crumble beneath his influence.
On the other hand, Demise himself has a similar backstory. He had mustered an army beneath his banner and set out to subjugate Hyrule in its early stages. Only by the influence of the Goddess Hylia was his invasion quashed, and Demise was sealed within another world. His own powers include summoning an electrical surge into his sword, which he then released (likewise to Ganon's orbs, I might add), and becoming an enormous menace, not unlike Ganon Beast. Although his abilities seem limited, we might have only seen a small sample of them. After all, the biggest thing that sticks our to me is that it took a goddess to stop him originally.
The Master Sword marks yet another factor that demonstrates the equivalence between them. They can only be defeated by the Blade of Evil's Bane, thus Link must find it each time he confronts them. The MS is also tied in with the "curse of hatred" that Demise mentioned before he was sealed away within the blade. It seems Ganondorf is a reincarnation of Demise, and through that he appears to have more power than the Demon King. But could it be that they aren't so different in that way of looking at it?
Quite possibly, they are the same being.
Ganondorf is the stronger of the two; as you said he possesses the Triforce of Power which alone puts him on a higher caliber than any previous villain, even the big D himself. Now, I don't know the specifics, but I believe Ganondorf can only be defeated by one who wields a piece of the Triforce as well as the Master Sword itself. Demise only requires the Master Sword.
I believe that Ganondorf is stronger than Demise. In terms of battle, Demise can be killed by the Master Sword alone. Ganondorf, however, needs other weapons too like the Light Arrows in addition to the Master Sword.
Allow me to remind you both that in order for Link to have the strength to confront Demise, he needed to obtain all three Triforce pieces first. Then, and only then, would he be able to harness the full power that the Goddess Hylia would ultimately bestow upon him. Does this make Demise more powerful than Ganondorf? Not necessarily. I only don't see them being that much different in overall might.
I don't even know how you fool yourself into thinking this is true. Majora is by far, the weakest of them all. The Kokiri Sword alone is enough to defeat Majora. Pathetic. And Bellum and Malladus are not portrayed anywhere to be stronger than Ganondorf. Bellum and Malladus might be stronger than Demise, but not close to Ganondorf.
Again, I feel that you should be reminded of where the battle with Majora takes place. It's not Hyrule where this happens, but Termina, which is an alternate universe of sorts to Hyrule. Nevertheless, the only resemblances to be found are the similar designs between Hyrulean and Terminian inhabitants. Other than that, the land of Termina seems to have rules of its own—rules that don't require the same certain tools for its great evil to be overthrown. In this case, that evil would be Majora, the chaotic demon that spread pandemonium across Termina. It isn't bound by the same weaknesses as either Demise or Ganondorf, as it is an entirely different entity than them. But this is mainly pure conjecture on my part, yet I find it to be a very reasonable projection.
