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

Vanguard Growth & Income Investor (VQNPX Quick QuoteVQNPX - Free Report) has a 0.32% expense ratio and 0.3% management fee. VQNPX 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. With yearly returns of 11.7% over the last five years, this fund clearly wins.

Janus Henserson Forty Institutional (JACAX Quick QuoteJACAX - Free Report) . Expense ratio: 0.55%. Management fee: 0.48%. JACAX 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. This fund has managed to produce a robust 12.99% over the last five years.

T. Rowe Price Cap Appreciation Adviser (PACLX Quick QuotePACLX - Free Report) . Expense ratio: 0.97%. Management fee: 0.59%. Five year annual return: 10.54%. PACLX is categorized as an All Cap Value fund, and like the name suggests, invests across the cap spectrum in small-cap, mid-cap, and large-cap companies.

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.