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.

Fidelity Mid-Cap Stock Fund K (FKMCX Quick QuoteFKMCX - Free Report) : 0.73% expense ratio and 0.69% management fee. FKMCX is a Mid Cap Blend mutual fund, and usually features a portfolio with stocks of various styles and sizes, allowing for diversification within a strategy that focuses on mid cap companies. FKMCX has achieved five-year annual returns of an astounding 11.48%.

MFS Growth Fund R2 (MEGRX Quick QuoteMEGRX - Free Report) is a stand out amongst its peers. MEGRX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. With five-year annualized performance of 14.48%, expense ratio of 1.09% and management fee of 0.49%, this diversified fund is an attractive buy with a strong history of performance.

MassMutual Select Mid Cap Value Service Class (MLUYX Quick QuoteMLUYX - Free Report) : 0.81% expense ratio and 0.7% management fee. MLUYX is a Mid Cap Value mutual funds that aims to target medium-sized companies that possess strong value and income opportunities for investors. With a five-year annual return of 8.44%, 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.