Definately tornados!!! I have had nightmares about them all my life, a couple times a year.
Growing up in Tampa Bay FLA hurricanes never frightened me because there is a warning ... but not so with tornadoes. I have seen the aftermath of random tornados and it is very destructive. I have seen how (the aftermath not the actually tornado) they jump from street to street missing a house here and there and totally destroying others - no rhythm or reason.
and lately it just seems ALOT of natural disasters scare me, landslides, wild fires, floods,quakes,Katrina hurricane ect. ect. .... because they just seem so random and we have zero control over them.