You're wise to start investing early in your career. Investing has many facets including return on investment and risk. There are many different types of investments including stocks, municipal bonds, corporate bonds, mutual funds, and so on. Nobody can give you an intelligent answers, because there are too many variables.
Each of the Vanguard funds has its own risks and rewards. If, for example, you invested in the Diversified Equity fund, your return would have been .57% return on investment since inception. The energy fund would have returned 13.29% return on investment since inception. However nobody has a crystal ball. What if a foreign government nationalizes the energy assets in its country? How would that effect your investments?
John, I would start by educating myself on the economic, financial, and psychological aspects of investing. There is an excellent primer on investing called Investing for Dummies. Please don't be offended by the name. For Dummies is a publishing company which puts out hundred of titles. They contact with authors who are knowledgeable, and have the ability to put concepts into plain English. This won't make you an investment expert, but it will give you the background to ask questions and understand the answers. Use this background to read more specialized books on mutual funds, psychological aspects of investing, factors that effect supply and demand, and so on.
Good luck, John.