Nobody mentioned here one important thing about keys, that advisers
recommend to do: try unusual keys to avoid cliches in your songs, for example this progression: C,G,Am,F
transposed half step down
will be this: B,F#,G#m,E
and if you play guitar then tablature
will be definitely different, you even will can't play what you
play in C key, so, your song will be another( maybe, closer to the next big hit)