As Raw said, it's damn hard to compare horses of different eras, and thumbs up to Chuck for having a go. For what it's worth, this would be my top 10:

01 - PHAR LAP
02 - TULLOCH
03 - KINGSTON TOWN
04 - BERNBOROUGH
05 - CARBINE
06 - MAKYBE DIVA
07 - MANIKATO
08 - MIGHT AND POWER
09 - PETER PAN
10 - RISING FAST