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

JPMorgan US Small Company I (JSCSX Quick QuoteJSCSX - Free Report) : 0.95% expense ratio and 0.6% management fee. JSCSX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. JSCSX has achieved five-year annual returns of an astounding 10.87%.

MFS Union Standard Equity Fund B (MUSBX Quick QuoteMUSBX - Free Report) : 1.49% expense ratio and 0.4% management fee. MUSBX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. MUSBX, with annual returns of 14.51% over the last five years, is a well-diversified fund with a long track record of success.

RBC SMID Cap Growth I (TMCIX Quick QuoteTMCIX - Free Report) . Expense ratio: 0.82%. Management fee: 0.7%. Five year annual return: 14.35%. TMCIX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion.

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.