Which discipline should I pick and why?
The one you are more interested in. Because you'll enjoy it more.
If you want to check out what jobs are available, browse the websites of companies that hire ChemEs (lots of industry) and NEs (power plants) and see what they have to offer. You can also check job search sites like monster.com, although those might often be a repost of things found directly. Other places to check are career fair websites (particularly any at your school) and to ask the career center at your school who has been hiring graduates of those two majors.