If you're invested in any of the funds in our "Magnificent Retirement Mutual Funds" list, congratulations on owning some of the best managed and top-performing mutual funds. If you are lucky enough to discover our list of Top-Ranked Funds for the first time, it's never too late to start investing with the best, especially when it comes to your retirement.

Great performance, diversification, and low fees: it's a pretty simple formula for a great mutual fund. Some are better than others, but utilizing our Zacks Rank, we have identified three mutual funds that would make great additions to long-term investors' portfolios.

Let's break down some of the mutual funds with the highest Zacks Rank and the lowest fees.

Principal Mid Cap Institutional (PCBIX): 0.7% expense ratio and 0.58% management fee. PCBIX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. With annual returns of 13.33% over the last five years, this fund is a winner.

MFS Mass Investors Growth Stock R1 (MIGMX): 1.48% expense ratio and 0.33% management fee. MIGMX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. MIGMX, with annual returns of 13.14% over the last five years, is a well-diversified fund with a long track record of success.

MSIF Global Franchise A (MSFBX) is an attractive large-cap allocation. MSFBX is a Global - Equity mutual fund, which invests their assets in large markets, leveraging the global economy. MSFBX has an expense ratio of 1.17%, management fee of 0.76%, and annual returns of 11.09% over the past five years.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.

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