LensRental Blog has access to thousands of lenses being used by their customers. With that rare opportunity, they've published some common problems of these lenses after heavy use. NOTE: the data reflects lenses that have been heavily used in harsh condition after 40 weeks.
Even though they claim there is no conclusion as to which lens is most reliable, it still interesting to know which lens most likely will develop problem after heavy use. Imagine investing in new lenses for a long term project in Vietnam where it's hot and humid. Good to know.