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.

The easiest, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

Elfun Trusts (ELFNX Quick QuoteELFNX - Free Report) : 0.18% expense ratio and 0.14% management fee. ELFNX 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. ELFNX has achieved five-year annual returns of an astounding 13.46%.

Ivy Mid Cap Growth I (IYMIX Quick QuoteIYMIX - Free Report) . Expense ratio: 0.79%. Management fee: 0.77%. IYMIX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. This fund has managed to produce a robust 15.35% over the last five years.

AB Lg Cap Growth Z (APGZX Quick QuoteAPGZX - Free Report) is an attractive large-cap allocation. APGZX 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. APGZX has an expense ratio of 0.5%, management fee of 0.48%, and annual returns of 15.98% over the past five years.

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.