I think whatever would adversely affect the most people. Personally, I don't know. I guess I don't think of them as realistically happening to me. I live in 'Tornado Alley,' but between the number of warnings as opposed to actual tornadoes (much lower ratio with modern technology), and having grown up watching storms with my Dad, near the basement
, I don't feel very threatened.
Of people I've talked-to, over the years, most seem to have the greatest fear of natural disasters that happen in areas other than where they grew up. Midwesterners fear earthquakes, west-coasters fear tornadoes, for instance. A case of the known versus the unknown, I think.
If the 'disaster' happens somewhere where people aren't affected, I can greatly enjoy the beauty of nature's extremes. Watching something on tv, for instance.
I guess I do have some fear of wildfires, if I was somewhere I couldn't get away. I saw some during 'the season' during the year I lived in San Diego (things weren't so extremely dry as they are now, so it wasn't such a constant threat), and they were beautiful in their way but scary when they got too close for comfort. Fortunately, I wasn't around for any that destroyed homes, for instance.
Humans tend to live in dangerous places, because those places are attractive for other reasons, and take the risk of whatever may happen in their region (I'm thinking fault-line areas, for instance).
Rambling; sorry 