A minor will usually involve mostly lower-division classes and just a handful (1-3 is pretty common) of upper division classes. It's a great way to pick up some extra skills--for example, if your major is something that is risky job-wise, a computer science minor can provide a good fall-back (you won't get a top software engineering job straight out of school with one, but you'll likely find something that will pay the bills a *lot* better than food service while you wait for your "real" career to take off)--or to satisfy some curiosity.
A double major is better if you're really super-interested in both fields. Maybe, for example, you want to do something interdisciplinary after you graduate. I was a double major in math and philosophy, and planned to enter a graduate interdisciplinary program in logic and cognitive science (although I ended up going a different direction). If you really need that kind of immersion, a minor won't give it to you.
The top double major combinations for men are as follows:
Two Different Business Majors
Economics and Engineering
Economics and Political Science
Economics and Foreign Language
Economics and Mathematics
Engineering and Mathematics
Economics and Business
Political Science and Philosophy
Engineering and Computer Science
Foreign Language and International Studies.
The most popular double major combinations for women are:
Foreign Language and International Studies
Foreign Language and Political Science
Foreign Language and Psychology
Foreign Language and Human Development
Foreign Language and Biology
Foreign Language and Business
Two Different Business Majors
Art and Psychology
Foreign Language and English
Biology and Psychology
Some universities require a minor and some don't. Mine did not. If a minor is required or just an option, that could often be a subject that you have an interest in that may or may not enhance your future career goals.
Examples of these types of majors are biology and marine biology, or history and social studies. If you select majors that are similar, it's may be possible to complete both majors within a four year span of time.
However, if the majors are not similar, then you may be need to extend your time as an undergraduate student to fulfill the requirements of both majors.
Minors are helpful for students that would like to obtain knowledge in a specific subject area, but not necessarily earn a degree. The benefit of a minor is that they are generally fifteen to eighteen credits in a specific subject area. Minors may also compliment a major possibly making a student more marketable when searching for employment.
Biology majors will often add minors in business, psychology, literature, or public health. These minors may allow the students application to a professional graduate program to stick out amongst students that submit traditional applications.
Business majors will consider minors in criminal justice, paralegal studies, or psychology, as these fields tend to compliment each other.