Jeez, I forgot to pimp Captain Kirk when talking about smartest. I mean, the dude is captain of the baddest starship in the universe. He's the only cadet to ever "solve" the Kobayashi Maru problem.
So, yeah... this one should be pretty much a landslide. Einstein + Bill Russell + Captain Kirk = a whole lotta win.
And while Spock was touted for his genius and logic, (untainted by emotion), Kirk actually solved many more of the problems and quandries that faced the Enterprise on it's journey throughout the cosmos, and Spock even turned to Kirk for answers when his "pure logic" proved too limited. (Oh yeah ... Kirk also beat Spock regularly in 3D chess). Genius of the highest order. How can any "Smartest" list beat one with Einstein, Zeus, Kirk, Merlin, and Bond on it? An absurdly obvious pun, I know, but this is a "no-brainer", IMHO. 
Suck up.
What can I say?!? Kirk, my favorite TV character, (and show) of all-time ... Einstein, my favorite thinker ... Merlin, my favorite mythic figure since childhood, (Camelot - he doesn't age, he youthens) ... and Uncle Bill, the definition of Basketball I'Q.. Sorry, this team is just plain stacked with brains, wisdom and favorites for me ... but "suck-up"? That's one thing I've never been accused of here, lol! (I'll take it as a compliment in this case). TP
Kirk's method solving problems: Throw mud at the wall and see if it sticks. He wasn't that smart, he just had the benefit of creative script writers!

So are you dissing the
character "Kirk" or the
writers? Any character is only as smart as his writers allow, so we could apply this rule to any other character on TV or Movies, (as in, I've seen many rather unintelligent actors get intelligently-written scripts). As far as the
character "Kirk", though, he actually solved more problems in the 78 episodes he was part of than Spock did.
Like the conductor of a symphony, a great Starship Captain must know all the jobs of his crew nearly as well as they do, ("The Corbomite Maneuver", "Arena", "City On The Edge Of Forever", "Miri", "A Piece Of The Action", "Assignment Earth", on and on ... most of the positive outcomes in TOS were a result of Kirk's ingenuity ... Spock just filled in the blanks along the way, (while Bones whined and Scotty blew a gasket!).