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.

Fidelity Select Semiconductors (FSELX Quick QuoteFSELX - Free Report) : 0.68% expense ratio and 0.53% management fee. FSELX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. FSELX has achieved five-year annual returns of an astounding 23.47%.

JPMorgan US Equity Fund R2 (JUEZX Quick QuoteJUEZX - Free Report) : 1.19% expense ratio and 0.4% management fee. JUEZX 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. JUEZX, with annual returns of 11.58% over the last five years, is a well-diversified fund with a long track record of success.

Lord Abbett Growth Leaders F (LGLFX Quick QuoteLGLFX - Free Report) . Expense ratio: 0.66%. Management fee: 0.51%. Five year annual return: 10.81%. LGLFX 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.

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.