Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

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 break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

William Blair Large Cap Growth N (LCGNX Quick QuoteLCGNX - Free Report) has a 0.9% expense ratio and 0.6% management fee. LCGNX 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. With yearly returns of 16.78% over the last five years, this fund clearly wins.

American Funds Mutual F1 (AMFFX Quick QuoteAMFFX - Free Report) : 0.64% expense ratio and 0.23% management fee. AMFFX is a Large Cap Value fund. These funds invest in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. AMFFX, with annual returns of 10.49% over the last five years, is a well-diversified fund with a long track record of success.

T. Rowe Price Mid-Cap Value (TRMCX Quick QuoteTRMCX - Free Report) : 0.8% expense ratio and 0.64% management fee. TRMCX is a Mid Cap Value fund, which usually invests in companies with a stock market valuation between $2 billion and $10 billion. With a five-year annual return of 14.26%, 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.