CSI:LV- If I was a guy, definitely Greg's. I've got a thing for his hair. Nick's is everchanging and weird but I wouldn't want it. As for girls, Sofia's. I like long hair, and her's is sleek and definitely kept well.
CSI:Miami- Calleigh's. For pretty much the same reason as Sofia's, actually; long hair, kept well, and Calleigh can wear her hair any way she wants -- wavym straight, up, down, in pigtails -- and it looks good.
CSI:NY- Aiden's, because it's just so effin' amazing. Stella's is too curly and I've already got Lindsay's style. As for guys on that show, I'd like to have Flack's. Why? Because it's black and depending, it's either kept or sort of messy looking.