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

Fidelity Advisor Series Equity Growth (FMFMX Quick QuoteFMFMX - Free Report) : 0.01% expense ratio and 0% management fee. FMFMX 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. FMFMX has achieved five-year annual returns of an astounding 15.95%.

Hennessy Cornerstone Mid Cap 30 Investor (HFMDX Quick QuoteHFMDX - Free Report) . Expense ratio: 1.36%. Management fee: 0.74%. HFMDX 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. This fund has managed to produce a robust 13.16% over the last five years.

Janus Henderson Enterprise D (JANEX Quick QuoteJANEX - Free Report) : 0.8% expense ratio and 0.64% management fee. JANEX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. With a five-year annual return of 10.72%, 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.