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 Fidelity Select Insurance (FSPCX Quick QuoteFSPCX - Free Report) . Sector - Finance funds offer a stable, diversified approach to investing that focuses on the financial industry, an infamously large, complex, and heavily-regulated space. This fund is a winner, boasting an expense ratio of 0.81%, management fee of 0.53%, and a five-year annualized return track record of 13.23%.

Matthews Asia Small Companies (MSMLX Quick QuoteMSMLX - Free Report) . Expense ratio: 1.32%. Management fee: 1%. MSMLX is a Pacific Rim - Equity fund, which usually invest in companies with a big presence in the export-focused markets of Hong Kong, Singapore, Taiwan, and Korea. This fund has managed to produce a robust 13.19% over the last five years.

T. Rowe Price All-Cap Opportunities Fund (PRWAX Quick QuotePRWAX - Free Report) . Expense ratio: 0.79%. Management fee: 0.64%. Five year annual return: 14.86%. PRWAX 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.

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.