I always loved Emerald Weapon, because I love the green colour, and also, he actually gives you a great reward, compared to Ruby Weapon.

I mean, you need KotR in order to beat Ruby Weapon, and to get the Materia you need a Gold Chocobo - and then your prize is another Gold Chocobo?
WTF?
Emerald Weapon, on the other hand, hands over a full Master Materia set, and that's a damn sight better.