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.

The easiest way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund Rank of over 19,000 mutual funds, we've identified three outstanding mutual funds that are ideally suited to help long-term investors pursue and achieve their retirement investing goals.

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

Sound Shore Fund (SSHFX) has a 0.95% expense ratio and 0.75% management fee. SSHFX is categorized as an All Cap Value fund, and like the name suggests, invests across the cap spectrum in small-cap, mid-cap, and large-cap companies. With yearly returns of 15.26% over the last five years, this fund clearly wins.

American Funds Growth Port R5E (RGSFX Quick QuoteRGSFX - Free Report) : 0.15% expense ratio and 0% management fee. RGSFX 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. RGSFX, with annual returns of 12.82% over the last five years, is a well-diversified fund with a long track record of success.

Nuveen Quant SmallCap Equity Retire (TRSEX) is an attractive large-cap allocation. TRSEX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. TRSEX has an expense ratio of 0.66%, management fee of 0.4%, and annual returns of 16.32% over the past five years.

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.