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.

DFA US Large Company I (DFUSX Quick QuoteDFUSX - Free Report) : 0.08% expense ratio and 0.06% management fee. DFUSX 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 annual returns of 15.73% over the last five years, this fund is a winner.

Fidelity Advisor Energy Fund I (FANIX Quick QuoteFANIX - Free Report) : 0.73% expense ratio and 0.53% management fee. FANIX 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. With yearly returns of 16.09% over the last five years, FANIX is an effectively diversified fund with a long reputation of solidly positive performance.

O'Shaughnessey MarketLeadersValue I (OFVIX Quick QuoteOFVIX - Free Report) . Expense ratio: 0.54%. Management fee: 0.4%. Five year annual return: 13.33%. OFVIX 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.

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.