Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

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 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 Invesco Small Cap Value A (VSCAX). VSCAX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. This fund is a winner, boasting an expense ratio of 1.05%, management fee of 0.63%, and a five-year annualized return track record of 18.83%.

BlackRock Sustain Advntg LC Core A (BIRAX): 0.73% expense ratio and 0.4% management fee. BIRAX 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. With yearly returns of 13.26% over the last five years, BIRAX is an effectively diversified fund with a long reputation of solidly positive performance.

Baron Durable Advantage Retail (BDAFX Quick QuoteBDAFX - Free Report) . Expense ratio: 0.95%. Management fee: 0.65%. Five year annual return: 15.09%. BDAFX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers.

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.