Probably not the easiest question to answer... but...
What is your favourite Vocaloid?
For me I'd have to say Luka, just slightly above Miku, but only by a little bit.

Miku, if you couldn't tell already.

Miku, for me She's what got my attention and made me discover the Vocaloid family, so that certainly makes her special. And she just sounds so darn cute

But there are more and more really amazing voices between the Vocaloids now. Especially since Vocaloid V3 arrived.

I'm just getting to know Tone Rion now. She sounds close to Miku.
And ofcourse there's still talk about an english Miku, but I don't know how far they are with that yet (there's been talk for over a year I believe, so it may still be a while before she gets here)

Oh, and the twins Len and Rin are also pretty cool

Luka, mainly for an epic public blasting of Just Be Friends at someone's ex-boyfriend a while back. Miku @ the twins come in a close second.

Jeez, you like to ask the tough ones, don't you?
For me, it's a tie between Miku and Luka. Luka has a slammin' body, but Miku has hotter moves, and can be just as sexy without showing as much skin