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.

Dreyfus Strategic Value Y (DRGYX Quick QuoteDRGYX - Free Report) : 0.63% expense ratio and 0.6% management fee. DRGYX 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. DRGYX has achieved five-year annual returns of an astounding 12.26%.

MFS Mass Investors Growth Stock A (MIGFX Quick QuoteMIGFX - Free Report) is a stand out amongst its peers. MIGFX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. With five-year annualized performance of 14.11%, expense ratio of 0.71% and management fee of 0.33%, this diversified fund is an attractive buy with a strong history of performance.

T. Rowe Price US Equity Research (PRCOX Quick QuotePRCOX - Free Report) : 0.45% expense ratio and 0.33% management fee. PRCOX 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. With a five-year annual return of 13.16%, 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.