Let's meet the combatants:
Chief Science Officer of the USS Enterprise (NC-1701), Spock is unique in that his father is Vulcan and his mother is Human, inheriting the best and worst traits of both species. He developed a deep friendship with Captain James T. Kirk that would span a lifetime, including Spock's death, resurrection, and creation of an alternate timeline (long story).
* Able to keep a cool and logical head in many extreme circumstances
* Skilled in the martial arts and telepathic linkage native to Vulcans
* Loyal and capable of great compassion (when he's not hiding it under a veneer of logic)
* As extreme emotions are alien to Vulcan culture, it becomes difficult to handle when they emerge
* Represses his Human side too often
* Can miss seemingly obvious social/emotional cues
Security Chief and Tactical Officer on the USS Enterprise-D, Worf (Son of Mogh) was rescued by a Human couple after a Romulan attack left him an orphan. Worf rose to become a very respected member of both the Enterprise crew and Starfleet itself, in spite of the inherent challenges of being a Klingon (both in his own nature and the rocky history his race has had with the Federation).
* Loyal, honorable, and possessing great courage
* Extremely strong and durable
* Secretly a romantic and idealist
* His love of tradition and his species aggressive tendencies can make him off-putting
* As the biggest, strongest guy in the room, he is often the first to be made an example of by powerful enemies
* Comes off as humorless (though he isn't entirely)
Both combatants are Token Alien Teammates who must struggle with adapting their own culture to the culture of their crew. As such, this will basically boil down to whether you prefer the Original Series or Next Generation. Or, if you're not a Trek fan, whether you put more stock into head or heart.
As always, make sure you're viewing the WEB version of the site and vote in the poll on the right-hand side of the screen. Poll closes Friday, and results posted on Saturday. Feel free to discuss your pick in the comments below.