There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

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 Advisor Equity Growth Z (FZAFX Quick QuoteFZAFX - Free Report) . FZAFX 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. This fund is a winner, boasting an expense ratio of 0.59%, management fee of 0.52%, and a five-year annualized return track record of 19.37%.

Janus Henderson Europe Focus I (HFEIX Quick QuoteHFEIX - Free Report) is a stand out amongst its peers. HFEIX is a Europe - Equity mutual fund investing in stocks across the vast European continent. With five-year annualized performance of 13.72%, expense ratio of 1.05% and management fee of 1%, this diversified fund is an attractive buy with a strong history of performance.

Advisory Research Allocation Cap Value (ADVGX Quick QuoteADVGX - Free Report) : 0.94% expense ratio and 0.7% management fee. ADVGX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. With a five-year annual return of 10.56%, this fund is a well-diversified fund with a long track record of success.

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.