Woah man, posting this 4 years ago would result in thermonuclear warfare. Risky.
Graphics: Twilight Princess
There's a 5 year time gap, but even still I prefer Twilight Princess. It was the most realistic visual representation of an actual world in a Zelda game. The lighting and water effects were brilliant for its time and the dark undertone to the style was a nice touch to represent the more mature themes in the game.
Soundtrack: Twilight Princess
No contest in my opinion. I think back, it's been 5 years since I last played either, and I hardly remember any Skyward Sword tracks. On the other hand, I could probably list all of TP's tracks if I wanted to. I put this mainly down to SS's transition into a more orchestrated soundtrack, which didn't exactly enhance the experience, but made you less associate music with key moments in the games.
Story: Twilight Princess
Another no contest. Skyward Sword's plot tried to weave in some really emotional moments, but it's quite often immature tone really made these moments fall flat. TP's darker tone (soundtrack and visual style) fit with its more mature themes. Yes it still had those whimsical Zelda moments, but the it made you feel for characters like Ralis, Colin, Ilia who weren't even main central characters. Then the character development of Midna and her whole arc. It was the most I've ever felt emotionally attached to the story and characters in a Zelda game. That is t saying too much, but still it's the pinnacle. Maybe only Majora's Mask can top it in this aspect.
Overworld: Twilight Princess
Skyward Sword was basically a hub with three levels. A disconnect overworld. More abundant, but not whole and rather claustrophobic at times. TP's Hyrule, while not perfect, was a complete world with transitioning landscapes. The wonder of seeing landmarks off in the distance and knowing you can travel there: Hyrule Castle, Death Mountain, the Bridge of Eldin etc. There was no feeling of that kind of discovery and granduar in Skyward Sword- it's indisputable.
Dungeons - Twilight Princess
TP dungeons did err on the side of bring too easy, but then you have the Lakebed Temple, Snowpeak Ruins and City in the Sky which id name as some of the toughest 3D dungeons in the series. Most of all though, it was the scale of the dungeons. Skyward Sword's dungeons felt underwhelming in scale. I want a dungeon to be something that completely dwarfs me; something that intimidates me; something that I can get lost in.
Bosses: Skyward Sword
Pretty easy. Twilight Princess while having probably the most visually appealing bosses, simultaneously had the worst. They were so mindnumbingly boring and repetitive. It's an insult to have all that build up and to see something so visually daunting turn out to be so weak. Skyward Sword was a step in the right direction of making bosses more dynamic and tactical.
Combat: Twilight Princess
I simply don't like the motion controls. They're tedious. Combat should be fluid, quick and satisfying. Motion controls just don't offer this sort of efficiency. Enemies that should be easy, become a hinderance after your ****ing billionth encounter with them. I found myself actively avoiding combat. Twilight Princess was simplified, but with the addition of sword techniques and Link's movement offered a surprise amount of depth.
Characters: Twilight Princess
Pretty much the same as I said in the story section. I felt more emotionally attached to the characters. Colin being like a younger brother who looks up to you, Ilia being that childhood friend you'll always protect, Midna being that someone who is completely different to you in every way but you still adore. So many characters had this sort of connections and the game weaves plot elements to develop Link's relationship with them. It makes you care so much more about the grand scope. You want to avenge the hurt that Ganondorf and Zabt have caused - you have a motivation. Skyward Sword? I didn't feel particularly attached to anyone bar Zelda who disappeared for most of the game as is custom.
Pacing: Twilight Princess
A tough one because I think both suffer from pacing past the half way point. Difference is, Twilight Princess' story develops more at this stage. Plus Skyward Sword's second half was comprised of retracing your steps. The wonder of adventure and discovery sort of wore off for me. Twilight Princess had that whole plot about the three ancient temples hidden away, which immediately put me back into "let's go adventure some more!".