Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

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 break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Alger Focus Equity A (ALAFX Quick QuoteALAFX - Free Report) : 0.91% expense ratio and 0.52% management fee. ALAFX 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. ALAFX has achieved five-year annual returns of an astounding 19.57%.

Invesco Technology Fund Investor (FTCHX). Expense ratio: 0.9%. Management fee: 0.58%. FTCHX is part of the Sector - Tech mutual fund category that invests in technology and lets investors own a stake in a notoriously volatile sector, but with a much more diversified approach. This fund has managed to produce a robust 14.97% over the last five years.

Oberweis Small-Cap Opps Instl (OBSIX). Expense ratio: 0.99%. Management fee: 0.8%. Five year annual return: 14.06%. OBSIX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets.

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.