Well here in old 150-plus-inches-of-rain-a-year Hilo, guitar string life can be measured with a stopwatch. There's only one way to keep something dry in Hilo, and that's to drive it across the island to Kona. So I'll give a big vote for humidity killing strings in a hurry. Seriously, you can hear the difference in a matter of a month or two. (They don't break, they just sound like wet newspaper and feel like a lead pipe.)

Aloha,
Mark