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

If it's songs you are hearing on the radio, probably the key was selected to fit the singer's vocal range better. In other words, it may have been transposed from the key the songwriter first wrote it in.

On the other hand—certain keys are favored in certain types of pop music because they fit well on the guitar and bass. And a good songwriter is going to be at home in any key; but certain keys feel different depending on your own associations with them and how hard they are to play on your own instrument, e.g. So I might very well reach for a "difficult" key depending on the emotional quality I want the song to have. Just my luck if it gets transposed for the singer anyway. ;-)