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They're all pretty horrible. Some are just beyond awful, like When Time Ran Out (1980), but even the "good" ones are dreadful. I suppose many would argue Airport, The Poseidon Adventure, The Towering Inferno and Titanic represent the best the genre has to offer, but even those four are bad movies I wouldn't waste any time on again.
My answer is none of 'em.
Airplane!, the hysterical spoof of the genre using 1957's Zero Hour as its main template, is the only disaster-related movie worth watching. And it should be seen over and over and over.
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"Film is a disease. When it infects your bloodstream it takes over as the number one hormone. It bosses the enzymes, directs the pineal gland, plays Iago to your psyche. As with heroin, the antidote to Film is more Film." - Frank Capra