Greg because:

Chamilionic hair or however you spell it
CUTE
HOT
funny
gives the expressions that make you melt and want to scoop him up in your arms and give him a HUGE HUG
relieves all the tension in the team:o :o :o

Favourite quote of his
Greg: Im just like a sponge i absorb information
Grissom: I thought that was my line?
Greg: Yer and i absorbed it