The better villain? Zant was cool and creepy but his true self was kind of a let down for me. Ghirahim went from creepy, to creepier, to just plain epic. Much more personality and I like what they did with him in the end.
Zant was awesome at the start of the game, but then, just like you said, his true personality was pathetic. Ghirahim, he's so weird, that tongue is creepy and overall has a scary personality. So Ghirahim for me.