I've heard it pronounced both low_high and high_low. Can anyone explain the meaning/reason behind the variation? (ie. difference in nuance, formal/casual, regional dialect, etc.) Ideally, I'd like to focus on one pronunciation to learn as a "standard" or "preferred learning pronunciation" if such a thing exists. よろしくお願いします！
ズボン is one of the words that is pronounced differently depending on the speaker. Typically it's pronounced as ズボン【HLL】, but elder people tend to prefer ズボン【LHL】. Both pronunciations are widely accepted. If you want to learn only one, I personally recommend ズボン【HLL】.
(Source: 『NHK日本語発音アクセント辞典』改訂 調査結果にもとづく作業方針の検討)