I personally, would have to say the ghost. For a few reasons. The first being its the games most important units says the Game itself. Second if you think about units that counter which units, the ghost is sadly the only attacking unit that doesnt counter anything well. Sure, he has the ability to drop nuclear missles but with 45 life 2-3 hits from just about any unit will kill him and the nukes take like 10 seconds to drop.. plus you cant very well hide the fact your dropping a nuke cause well 2 reasons. One, it puts a red dot where ever your nuking, and 2 the game announces this susposid secret. Seems to me, if ghost is the games most important unit it shouldnt suck so damn much.