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.

Empower Large Cap Value Inv (MXEQX): 0.96% expense ratio and 0.59% management fee. MXEQX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. MXEQX has achieved five-year annual returns of an astounding 11.24%.

Goldman Sachs MLP Energy Infrast R6 (GLPSX Quick QuoteGLPSX - Free Report) : 1.04% expense ratio and 0.96% management fee. GLPSX is classified as a Sector - Energy mutual fund. Throughout the massive global energy sector, these funds hold a wide range of quickly changing and vitally important industries. GLPSX, with annual returns of 21.92% over the last five years, is a well-diversified fund with a long track record of success.

Nuveen Quant SMid-Cap Eq R6 (TSMWX) is an attractive large-cap allocation. TSMWX is a Small Cap Blend mutual fund that usually targets companies with a market capitalization of less than $2 billion. TSMWX has an expense ratio of 0.46%, management fee of 0.42%, and annual returns of 11.6% over the past five years.

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.