It's hard to choose cause they're both very talented musicians, but Hyde always wins out in the end for me.....his voice is so strong and passionate (like in Niji or Heaven's Drive) but other times it's soft and lullaby-like (like in his Reontgen series). Hyde's voice can reach pitches and nuances that Gackt's voice just can't. Plus i think Gackt's voice is a little nasaly and doesn't change much from song to song. His 'Diabolos' album got really boring after a while.
As for looks....they're both pretty hot, but again Hyde wins out. Gackt's too plastic for my tastes ^^
Elanor- is it something with us aussies? Kasou owns my soul too