I say Vulcan's are lebih logical. I base this entirely on Brent Spiner's performance as Data. If anda watch him closely, Data is very eager to be human and because of this he is willing to make himself look foolish and illogical on many occasions. So based on behavior, Vulcan's act way lebih logical.
Although Data's positronic brain is designed to imitate a human brain, throughout the series he is shown to struggle with his inability to experience emotions. Although he demonstrates creativity through improvisation, original ideas and ingenuity, most of his behaviors seem strictly rational.
Vulcan logical thinking is a learned trait, requiring social practices and personal effort to subdue their very strong natural emotions. Spock is only half Vulcan, and although he has adopted their way of life he does experience conflict between his ideal logical state and lapses of irrational behavior.
Thus, Data is a logical being attempting to overcome a purely logic-based perception, and Spock is an emotional and feeling being continually making a conscious effort to operate according to logical principles. Spock is logical-like, Data is logical with aspirations to be otherwise.
"As anda examine your life, do anda find anda have missed your Humanity?" "I have no regrets." "'No regrets.' That is a Human expression." "Yes. Fascinating."
Although Spock and Data have not gone head to head, I do know that when Picard wanted to argue with some Vulcan staff in the episode "Sarek" he sent Data to do it for him after his own attempt failed and Data succeded. Yes Data can out logic Vulcans. I'm thinking (pre emotion chip Data) could beat Spock after a long battle.
I think that Spock is the lebih logical one because of his Vulcan upbringing. Even though he is half-human the Vulcan half seems to be the most promanent. Data tries to behave like a human and that makes him a little less logical.