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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

MFS Blended Research Core Equity A (MUEAX Quick QuoteMUEAX - Free Report) has a 0.63% expense ratio and 0.25% management fee. MUEAX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. With yearly returns of 13.92% over the last five years, this fund clearly wins.

T. Rowe Price US Large-Cap Core I (RCLIX): 0.57% expense ratio and 0.53% management fee. RCLIX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. With yearly returns of 11.84% over the last five years, RCLIX is an effectively diversified fund with a long reputation of solidly positive performance.

Transamerica Large Cap Value I2 (TWQZX) is an attractive large-cap allocation. TWQZX 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. TWQZX has an expense ratio of 0.63%, management fee of 0.59%, and annual returns of 12.57% over the past five years.

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.