It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

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

If you are looking to diversify your portfolio, consider Franklin Convertible Securities Adviser (FCSZX Quick QuoteFCSZX - Free Report) . FCSZX is categorized as a Convertible Bonds fund, and in the fixed income world, these funds are quite unique. These types of securities are a hybrid, meaning they have components of both fixed income and equity. This fund is a winner, boasting an expense ratio of 0.58%, management fee of 0.45%, and a five-year annualized return track record of 9.86%.

Hartford Stock HLS IA (HSTAX Quick QuoteHSTAX - Free Report) : 0.51% expense ratio and 0.48% management fee. HSTAX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. HSTAX, with annual returns of 10.91% over the last five years, is a well-diversified fund with a long track record of success.

MainStay Large Cap Growth R1 (MLRRX Quick QuoteMLRRX - Free Report) : 0.81% expense ratio and 0.61% management fee. MLRRX 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. With a five-year annual return of 11.37%, this fund is a well-diversified fund with a long track record of success.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.