Fly came first, Dead Sound of Misery is a remix, like JoshPR said. I would definitely say I like Fly better because I liked Fly very quickly, and still do after many listens, but Dead Sound Of Misery, which I originally didn't like (even though I loved Fly at the time, and was unaware it was a remix) has only come to be considered a mediocre song for me.
Fly came first, Dead Sound of Misery is a remix, like JoshPR said. I would definitely say I like Fly better because I liked Fly very quickly, and still do after many listens, but Dead Sound Of Misery, which I originally didn't like (even though I loved Fly at the time, and was unaware it was a remix) has only come to be considered a mediocre song for me.