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 take a look at some of our top-ranked mutual funds with the lowest fees.

Westcore Small-Cap Growth Retail (WTSGX Quick QuoteWTSGX - Free Report) has a 1.03% expense ratio and 0.65% management fee. WTSGX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With yearly returns of 12.16% over the last five years, this fund clearly wins.

Congress Mid Cap Growth Retail (CMIDX Quick QuoteCMIDX - Free Report) : 1.04% expense ratio and 0.6% management fee. CMIDX is a Mid Cap Growth mutual fund. These funds aim to target companies with a market capitalization between $2 billion and $10 billion that are also expected to exhibit more extensive growth opportunities for investors than their peers. CMIDX, with annual returns of 11.3% over the last five years, is a well-diversified fund with a long track record of success.

Capital Group US Equity (CUSEX Quick QuoteCUSEX - Free Report) . Expense ratio: 0.43%. Management fee: 0.42%. Five year annual return: 10.75%. CUSEX 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.

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.