The 'best' songwriter is the one who floats yer personal boat.
Mine are:-

1) His Majesty Stan Rogers
2) Archie Fisher
3) Maggie Holland (she's a female BTW!) :0)
4) Allan Taylor
5) Sally Barker (ex-poozies and another female) :0)
6) Kylie and Emma Bunton (they don't write songs but they do float my boat) :0)

Johnny :0)