All of them except Spock have major flaws.
Riker is DISGUSTING. Remember when he seduced the sex-less person?
Kira has a rage problem. Understandably so, but still.
Chakotay is nothing more than a hilarious stereotype.
T'Pol...

... Oh, T'Pol. Why does she wear three-inch heels aboard a Starship?
SPOCK is a dreamboat and a half! Plus, he's DEEP. PLUS, if he's good enough for Nurse Chapel, he's good enough for me.
HOWEVER... I'm voting for Chakotay for the simple fact that ROBERT BELTRAN IS A PROVERBIAL PIMP! If you don't believe me, watch this movie ASAP:
http://en.wikipedia.org/wiki/Night_of_the_Comet
Oop, here's a clip:
http://www.youtube.com/watch?v=7DAJ-DK540E