How to select a key-signature for a song?

Question

There are so many songs in pretty odd key-signatures like 4,5,6 sharps or flats. At least this is my impression when I listen to songs on the radio/net while trying to follow them on my piano/guitar. I can understand that some instruments prefer certain ranges of the circle of fifths, nevertheless ... - are songs really "written" in the keys you hear on the radio/CD/... - why do composers make their lives so difficult, why don't they use "easier" keys? - what are the criteria for a composer (today - tempered tuning) to select a key for a song

Answer 1

It really depends on what the composer or songwriter feels like writing. Some melodies hold deeper meaning in one key than the other. For singers specifically, some keys allow for different parts of the voice to be more resonant than others. For example, the key of F (1 flat) vs. the key of F sharp (6 sharps) can be a world of difference to a singer in their resonance and their vocal flexibility. A lot of composers today don't even write in keys, using atonal techniques.