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 investors' portfolios.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

If you are looking to diversify your portfolio, consider Fidelity Stock Selector Allocation Cap (FDSSX). FDSSX 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 0.53%, management fee of 0.49%, and a five-year annualized return track record of 12.64%.

AQR Global Equity Fund N (AQGNX Quick QuoteAQGNX - Free Report) is a stand out amongst its peers. AQGNX is a Global - Equity mutual fund. These funds invest in large markets like the U.S., Europe, and Japan, and operate with very few geographical limitations With five-year annualized performance of 15.01%, expense ratio of 1.04% and management fee of 0.6%, this diversified fund is an attractive buy with a strong history of performance.

Goldman Sachs International Equity Insights Service Class (GCISX): 1.3% expense ratio and 0.75% management fee. GCISX is a part of the Non US - Equity fund category, many of which will focus across all cap levels, and will typically allocate their investments between emerging and developed markets. With a five-year annual return of 11.34%, 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.