overshooting is the scariest imho
undershooting is imho usually more painful but as mentioned before, you have so much time to think when you overshoot, it's fucking with your head :P
anyways, my most recent 'oh fuck' moment was when i was leadclimbing and was about 15ft above my last bolt and if i slipped i was pretty sure i was gonna hit some nasty protruding rocks below the bolt and it was just in the hardest section of the route, i was completely cramping up but i knew falling was a really bad idea so i somehow pulled through anyways, i don't think i've ever been so happy of clipping into the next bolt :P
my belayer said he had never seen someone clip a quickdraw as fast as i did then :D
i'm usually pretty level headed when lead climbing 'exposé' routes but i just knew this could've gone so wrong, it was by far the most scared i've ever been on a route ...