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.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

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

Davis Appreciation & Income Y

(DCSYX Quick QuoteDCSYX - Free Report) : 0.67% expense ratio and 0.55% management fee. DCSYX is an Allocation Balanced mutual fund. Allocation Balanced funds look to invest across asset types, like stocks, bonds, and cash, and including precious metals or commodities is not unusual; these funds are mostly categorized by their respective asset allocation. DCSYX has achieved five-year annual returns of an astounding 11.8%.

MFS Growth Fund R2

(MEGRX Quick QuoteMEGRX - Free Report) is a stand out amongst its peers. MEGRX 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 five-year annualized performance of 14.57%, expense ratio of 1.07% and management fee of 0.5%, this diversified fund is an attractive buy with a strong history of performance.

State Street Institutional US Equity Services

(SUSSX Quick QuoteSUSSX - Free Report) : 0.64% expense ratio and 0.39% management fee. SUSSX 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. With a five-year annual return of 16.79%, this fund is a well-diversified fund with a long track record of success.

There you have it. If your financial advisor had you put your money into any of our top-ranked funds, then they've got you covered. If not, you may need to talk.