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.

John Hancock Discipline Value Mid Cap Investor (JVMAX Quick QuoteJVMAX - Free Report) : 1.12% expense ratio and 0.71% management fee. JVMAX is a Mid Cap Value fund, which usually invests in companies with a stock market valuation between $2 billion and $10 billion. JVMAX has achieved five-year annual returns of an astounding 12.15%.

T. Rowe Price Mid-Cap Growth I (RPTIX Quick QuoteRPTIX - Free Report) : 0.63% expense ratio and 0.61% management fee. RPTIX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. With yearly returns of 9.68% over the last five years, RPTIX is an effectively diversified fund with a long reputation of solidly positive performance.

Deutsche Capital Growth A (SDGAX Quick QuoteSDGAX - Free Report) : 0.9% expense ratio and 0.46% management fee. SDGAX 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 a five-year annual return of 16%, this fund is a well-diversified fund with a long track record of success.

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.