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.

If you are looking to diversify your portfolio, consider MainStay MAP Fund A (MAPAX Quick QuoteMAPAX - Free Report) . MAPAX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. This fund is a winner, boasting an expense ratio of 1.02%, management fee of 0.66%, and a five-year annualized return track record of 12%.

Commerce Growth Fund (CFGRX Quick QuoteCFGRX - Free Report) is a stand out amongst its peers. CFGRX 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. With five-year annualized performance of 13.43%, expense ratio of 0.69% and management fee of 0.4%, this diversified fund is an attractive buy with a strong history of performance.

Buffalo Small Cap Fund (BUFSX Quick QuoteBUFSX - Free Report) . Expense ratio: 1.01%. Management fee: 0.85%. Five year annual return: 14.1%. BUFSX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets.

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.