I moan about the same thing myself! While everyone else's songs (whether complex or very simple) sound fantastic and lovely, I never think songs I sing, of my own or traditional, have the 'right' sound. I sing around and about and receive a positive response, but I am hugely lacking confidence as I always think I don't sound quite as good as the next person!

(And I play piano, so it's nothing to do with strumming technicalities that I don't really understand!!)