There is that thread SMG vs. Manual here on the forums and its a great debate. But SMG is the winner by far...unrivaled shift speeds (by any HUMAN, PERIOD. Its good for lazy around town traffic or at the track (more concentrating on driving and not heel-toe-ing....no worry about grinding gears when your trying to show off...flawless rev-matching...the list goes on and on.
However if this is a weekend car or driven only once a week or something then get stick and knock yourself out. (not literally,