Should I major in mechanical or chemical engineering?

In all honesty, MEs and ChEs can both do most of each other's jobs. However, the knowledge of chemistry is a pretty good advantage. The only time there might be minimal value in the knowing chem is if you specialize in machine design. Anyone who tries to tell you that a ChE has fewer options on location has no clue. There is also no difference in industries. Just knowing chem "separates the men from the boys"; you can pick up a lot of chem OTJ or in personal study, but what have you lost or given up? ChE is generally recognized as the most challenging degree to get. If you start to wash out of ChE, you can always change to ME, but it's harder to do the converse.