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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

Fidelity Select Software & IT Services (FSCSX Quick QuoteFSCSX - Free Report) : 0.68% expense ratio and 0.52% management fee. FSCSX 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 11.74% over the last five years, this fund is a winner.

Neuberger Berman Guardian Adviser (NBGUX Quick QuoteNBGUX - Free Report) : 1.17% expense ratio and 0.88% management fee. NBGUX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. With yearly returns of 10.71% over the last five years, NBGUX is an effectively diversified fund with a long reputation of solidly positive performance.

Ivy Large Cap Growth Y (WLGYX Quick QuoteWLGYX - Free Report) . Expense ratio: 1%. Management fee: 0.6%. Five year annual return: 11.07%. WLGYX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks.

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.