Zelda is a much better game. Quality is one of the strong points Nintendo games have. I don't have to play many hours into it, to find a broken quest line or something bizarre happening during gameplay. I know with Zelda I can play it and not have any problems and focus on playing a good game then worrying about bugs and graphical glitches and waiting for patches to fix things in the game. Not my idea of wanting to get involved with a game. I love the TES series, but there a mess on release days, and patches have to be waited on for the game that was just purchased. Bethesda always seems to release games riddled with bugs and other problems.
Bugs and glitches happen when you have a game with as much content crammed into it as Skyrim, on as many platforms.
Considering Zelda is almost entirely linear, with next to no open-world exploration, and is only on one platform, it is OBVIOUSLY going to have fewer bugs. That's just common sense.
The true power of Zelda is that it wields nostalgia like a warhammer. TES relies on a massive amount of content. As a consequence, it takes longer to make them, they're buggier, and it costs Bethesda more to make them.
Edit: That said, I did enjoy Twilight Princess. It was generally pretty fun, and had some good boss fights. But it, and any other Zelda game, will never be in the league of TES.