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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

American Century Select R (ASERX Quick QuoteASERX - Free Report) has a 1.46% expense ratio and 0.99% management fee. ASERX 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 yearly returns of 12.65% over the last five years, this fund clearly wins.

Fidelity Select Health Care Services (FSHCX Quick QuoteFSHCX - Free Report) is a stand out amongst its peers. FSHCX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy. With five-year annualized performance of 15.14%, expense ratio of 0.71% and management fee of 0.52%, this diversified fund is an attractive buy with a strong history of performance.

AMG Frontier Small Cap Growth N (MSSVX Quick QuoteMSSVX - Free Report) : 1.3% expense ratio and 0.7% management fee. MSSVX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With a five-year annual return of 14.03%, 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.