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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

Northern Active M Intlernational Equity (NMIEX) has a 0.85% expense ratio and 0.82% management fee. NMIEX is a Non US - Equity option, focusing their investments acoss emerging and developed markets, and can often extend across cap levels too. With yearly returns of 10.55% over the last five years, this fund clearly wins.

FMI Common Stock Institutional (FMIUX): 0.83% expense ratio and 0.79% management fee. FMIUX is a Mid Cap Blend mutual fund, and usually features a portfolio with stocks of various styles and sizes, allowing for diversification within a strategy that focuses on mid cap companies. FMIUX, with annual returns of 12.93% over the last five years, is a well-diversified fund with a long track record of success.

MFS Blended Research Growth Eq R6 (BRWVX Quick QuoteBRWVX - Free Report) is an attractive large-cap allocation. BRWVX 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. BRWVX has an expense ratio of 0.42%, management fee of 0.25%, and annual returns of 16.18% over the past 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.