Aa~, Duty, my favourite album!! ^_^ Pretty much my favourite because it has my two most favourite Ayu songs ever, but also because I think it has amazing flow, and the atmosphere the album gives off is incredible - something very distinct from every other album, for better or for worse.
Duty - This is my all-time favourite Ayu song. It's one of the most experimental pop tracks I've ever heard, and it's near perfect in every way. The haunting melody, the depressing lyrics... Totally my type of song, hah. Her lyrics are very squeaky here, but somehow, they're still.....dare I say, wonderful?? I really wish she did this song live in recent years.
vogue - Well, whaddya know! My second favourite Ayu song of all time, hah! XP The lyrics are what really kept hold of me in this one. I have so many regrets in life, and this is a song to me and everybody else with regrets: she's telling us that it's going to be okay, and that people who do us wrong will get what they deserve. And that's awesome, hah. This is also a really non-traditional pop song, which I love. The vocals are quite annoying....but despite that fairly major disturbance, I can't hate on this song, lol.
End of the World - This song used to be a high favourite, but not anymore. I still adore it, though. Again, really annoying vocals, but everything else makes up for it. I'm so glad she actually did this one live not too long ago.
SCAR - I've always found this one to be just okay. My third least favourite on the album... But it fits so well with the rest of the album, and I love that. It's also very relaxing, especially after the previous two songs, hah.
Far away - The beginning of this song really annoys me, lol. :X I do like it, but it's my second least favourite on the album. It also gets too much recognition, I feel, especially since it's tied in with the ultra-amazing SEASONS and vogue.... What?? >_>
SURREAL - I love this song, of course.

I feel it's one of her most interesting, because of the way it's set up and everything. The first time I heard it, I remember being so wowed at all the different "parts" of this song - so random, yet it works so well, hah. To this day, I can never get enough of the last 'part', with the 'la la~ la la!'s. XP
AUDIENCE - This song isn't bad, but I get so tired of it, really fast. Especially since it's a concert staple. Honestly, I REALLY think she should replace this one with something else... Anyhow, this is my least favourite song on Duty.
SEASONS - A classic!

This is just such a beautiful song, I find it hard to believe anybody couldn't like it.

I've never really gotten sick of this song, either, so that says a lot, especially since it's always been pretty high on my list.
teddy bear - Definitely another really high favourite of mine, right here! ^.^ Like Ayu, I also have some father issues, eh heh... And this song really gets to me sometimes. It's easily one of her most simplistic songs, yet it's unbelievably touching. I wish she did more songs like this (and like Curtain Call).
Key ~eternal tie ver.~ - It took me a long time to really appreciate this song. It's still not one of my most favourite songs, but I do like it a lot. And I love how the lyrics honestly aren't anything special....yet at the same time, they are. XD I don't know how to explain it, lol.
girlish - I've always really liked this one!

It's even better as an ending track, too - one of her best to date, I think. The semi-live quality makes it really memorable... And also, the beginning, with the "ACTION!" and giggling cracks me up, hah.