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 way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund Rank of over 19,000 mutual funds, we've identified three outstanding mutual funds that are ideally suited to help long-term investors pursue and achieve their retirement investing goals.

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

Congress Large Cap Growth Fund (CAMLX Quick QuoteCAMLX - Free Report) has a 0.93% expense ratio and 0.5% management fee. CAMLX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. With yearly returns of 10.56% over the last five years, this fund clearly wins.

Fidelity Select Tech Hardware (FDCPX Quick QuoteFDCPX - Free Report) : 0.72% expense ratio and 0.53% management fee. With a much more diversified approach, FDCPX--part of the Sector - Tech mutual fund category--gives investors a way to own a stake in the notoriously risky tech sector. FDCPX, with annual returns of 11.13% over the last five years, is a well-diversified fund with a long track record of success.

Oberweis Small-Cap Opportunities (OBSOX Quick QuoteOBSOX - Free Report) . Expense ratio: 1.25%. Management fee: 0.8%. Five year annual return: 13.35%. OBSOX 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.