If we're counting books, then Surak.
If we're only counting screen events, then it would be easier to say who wasn't a good Vulcan. Sarek, Soval, Tuvok, T'Pol, T'Pau (both versions), everyone from Amok Time, everyone from the end of ST: III, everyone from the DS9 baseball game - all good. The worst I can say for almost anyone who played a Vulcan is that they were boring
. And, well, they're Vulcan, so that isn't really a problem, is it?
Ironically, if I were going to pick the worst on-screen performance of a Vulcan, it would be Surak from TOS. But even that has an excuse - he was fake!
The worst thing any of the actors do is mistake attitude for stoicism from time to time, but that's mostly the long-term actors like Russ or Blalock, and really, pretty understandable. Especially for Russ. If I were on Voyager, I'd be pissed off all the time, too.