So, this is gunna be almost all anime. Just to give you all a bit of warning.
- which songs/themes/OPs/EDs/singers/groups/bands/etc (whatever you can think of) are your favorites and why
Favorite Opening - Hikari no Senritsu by Kalafina (Sora no Woto/Sound of the Sky). I like the simple but beautiful visuals (fancy slideshow of altered Klaus Badelt art) and the music (Kalafina and Yuki Kajiura? YES PLEASE)
Favorite Ending - Witch☆Activity by TECHNO BOYS PULCRAFT GREENFUND (Witch Craft Works). The music is catchy and the adorable chibi witches getting tortured in classic ways is much cuter than it rightfully should be.
Favorite Singer - Aya Hirano. She has a very powerful voice that I just love, and unlike most singers with a lot of vibrato in their voice (in my opinion, it's a necessity, but less is more), I actually like the large amount in hers. It also helps that she voices Lucy in Fairy Tail...
Favorite Group/Band - Kalafina. They have a very choral feel to their vocals and the music itself is a unique style I've never heard in other bands. I wish I did hear more of it, because it's beautiful.
Favorite Composer - Yuki Kajiura. A lot of her work has a very Kalafina feel to her music (given the fact the she is the creator/composer/a back up singer of Kalafina). I like her for the same reasons as Kalafina, but she can also be wonderfully versatile, as seen in her work on the opening theme of Baccano!
Favorite Soundtrack - The World Ends With You. It is a very diverse soundtrack, and one of the few game soundtracks that have complex songs with vocals instead of the less than a minute long instrumental bits played on repeat during battles or the main title page.
- which songs you consider the most touching/sentimental/emotional/etc
I don't really know what my favorites are right now, I'm currently in the middle of revising my list. DOA by Hiroyuki Sawano is the current #1, but that's gunna change once i start to mess with the lists order. there is a lot of Yuki Kajiura on the list though.
From a non-anime viewpoint, I also like the soundtracks of most Final Fantasy/Kingdom Hearts games, Disney movies, The Lord of the Rings/The Hobbit, and Pirates of the Caribbean.
- which songs/singers/soundtracks/etc. are your least favorite and why
Don't current'y have any least favorite singers or soundtracks, but my current least favored song is Let It Go by Idina Whatever from Frozen. I didn't care one way or the other for it at first, but then I kept hearing it over and over and over again, and now I'm just sick of it.