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.

AB Large Cap Growth K (ALCKX Quick QuoteALCKX - Free Report) : 0.97% expense ratio and 0.48% management fee. ALCKX 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 annual returns of 12.62% over the last five years, this fund is a winner.

Fidelity Advisor Technology M (FATEX Quick QuoteFATEX - Free Report) . Expense ratio: 1.22%. Management fee: 0.53%. FATEX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. This fund has managed to produce a robust 18.76% over the last five years.

Voya Growth & Income Portfolio S2 (IGISX Quick QuoteIGISX - Free Report) : 1.07% expense ratio and 0.6% management fee. IGISX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.51% 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.