While both are rather one dimensional, points go towards Ganondorf for being the most interesting. Also, I always thought Demise was a little over designed, like he's just trying too hard to be big and evil.
While I do like Ganondorf better overall, Wind Waker Ganondorf has Demise beat as far as one-on-one sword fights (and their conclusion) go.
Also, Ghirahim was more interesting to fight, I felt, as he used some tricks and constantly changed his tactic in the middle of it (plus having a personal grudge against you), instead of being a big burly dude with easily-blocked sword swings. It might also be because Demise (Imprisoned) looked like this for most of the game. I just can't take him/it seriously with that shape.
"It takes 43 muscles to frown, but only 5 to pull the pin out of a grenade." ~ Unknown
Ganondorf completely beats Demise in all aspects, especially in looks and story. I found Demise to be extremely boring and stereotypical. And I don't whats all the rave about his looks. He looked like a big and buff alligator with some fire hair. It didn't look good at all. On the other hand, I absolutely LOVE TP Ganondorf's looks and WW Ganondorf looked awesome as well.
Ganondorf is the only attractive male in the series.
Ganondorfs appeared more and his been more central to the games lore. Demise is retractively the first one and we dont know if hell appear again (we could get a game set earlier at the fall and imprisonment)
Honestly Im alot fonder of Vaati, even tho Ganon is the "main" villian.
Demise created the monsters, Vaati released them on Hyrule, Ganondorf became the 'main' villian and caused so much ruckas that time split. Its a decent progression of villians.
I would have to go with Ganondorf. I tend to like the villains more than the hero in most series like this mostly because they tend to have a few more layers to their character than the heroes. Villains normally have to have a good reasons to be villainous or at least some type of origin that set them on their evil path in life. Ganondorf has this even though it did take many years and appearances before that was finally brought to light and he became more than just a generic villain that simply loves doing bad things for the sake of being bad. He has now taken on the role of a somewhat sympathetic character that grew too greedy in his desire for everything the Hylians had.
Demise simply does not have this. In fact out of all the various villains to appear in the Zelda series I think he is the one we know the least about. He simply has not been around long enough to develop since Nintendo normally requires a few more sequels and publications before a character becomes a little more than one dimensional. But he is a character that appeared very late in his debut game, was only around for a very short time with minimal dialog and was then defeated. Leaving the players to not just fill in gaps, but basically use their imaginations to come up with just about everything. We know he was a high ranking demon lord, that this fiery humanoid appearance might not be his true form at all, and that he wants the triforce. To me this is only slightly more than what we knew about Ganon back in 1987. In my opinion that lack of knowing makes him less interesting, and his visual appearance vs previous villains can only go so far. He certainly looks more impressive than almost all of the other villains put together. But based on the fact that I know about as much of him as I do Bongo Bongo I do not find him to be as interesting as I do Ganondorf.
Watch this evolve into a SS vs. TP thread that the mods ignore for about three years. Not anything against you mods, but that's where it looks like this is headed.
Anyway, I don't care for either. Demise is a generic evil guy who's like, "HURRRR IME EVIL FEAR ME" which is laughable. Anybody who says that SS's villain was Demise is on crack; it's clearly Ghirahim. Ganondorf is yet another generic evil with barely any personality. "Herp a derp, Vainqueur, there was WW!" Yeah, yeah, yeah, he had 'emotions' in that game, which were the bare minimum of what you could call emotion. That and the fact he's appears only twice in most of the Zelda games makes him a laugh rather than a nightmare.
I wonder if theres an evil equivalent of the sacred realm where all the evil bosses meet and discuss things?
Bellum: Dam that Link!
Demise: Look I have an idea that might work!
Aghanim: My feet itch.
Zant: Wth is that smell?
Well I think that the dark World of ALTTP would be the equivalent to the Sacred Realm.
But I think that you have raised an interesting point. If that there could be some sort of underworld for Link to visit that contains past bosses from previous games that this current Link could try his luck against. It would be an amazing way to somehow include Twinrova, Blind the thief, Majora, Veran, Vaati, Argorok, etc all in a single game. Plus the theorists minds would explode at the chance to get any closer look at just how so many villains somehow manage to rise from the grave and return to Hyrule every few hundred years. Maybe even the poe collector could reappear somehow.
I think the series has had enough random undead, zombies, skeletons, ghosts, and demons to be capable of pulling this off without altering too much.