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, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

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 Series Intrinsic Opportunities (FDMLX Quick QuoteFDMLX - Free Report) . FDMLX 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. This fund is a winner, boasting an expense ratio of 0.01%, management fee of 0%, and a five-year annualized return track record of 13.54%.

Janus Henderson Contrarian T (JSVAX Quick QuoteJSVAX - Free Report) : 0.85% expense ratio and 0.6% management fee. JSVAX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. JSVAX, with annual returns of 11.72% over the last five years, is a well-diversified fund with a long track record of success.

Putnam Small Cap Growth B (PNSBX Quick QuotePNSBX - Free Report) is an attractive large-cap allocation. PNSBX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. PNSBX has an expense ratio of 0.98%, management fee of 0.73%, and annual returns of 11.3% 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.