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.

Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Fidelity Advisor Semiconductors A (FELAX Quick QuoteFELAX - Free Report) : 1% expense ratio and 0.53% management fee. FELAX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. With annual returns of 25.95% over the last five years, this fund is a winner.

GMO Quality IV (GQEFX Quick QuoteGQEFX - Free Report) . Expense ratio: 0.45%. Management fee: 0.44%. GQEFX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset. This fund has managed to produce a robust 12.46% over the last five years.

JPMorgan Growth Advantage I (JGASX Quick QuoteJGASX - Free Report) : 0.79% expense ratio and 0.55% management fee. JGASX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 14.44% over the last 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.