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.

If you are looking to diversify your portfolio, consider William Blair Large Cap Growth N (LCGNX Quick QuoteLCGNX - Free Report) . LCGNX 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. This fund is a winner, boasting an expense ratio of 0.9%, management fee of 0.6%, and a five-year annualized return track record of 11.03%.

Oberweis Small-Cap Opportunities (OBSOX Quick QuoteOBSOX - Free Report) . Expense ratio: 1.25%. Management fee: 0.8%. OBSOX is one of many Small Cap Growth mutual funds; these funds tend to create their portfolios around stocks with market capitalization of less than $2 billion. This fund has managed to produce a robust 15.98% over the last five years.

Victory Sycamore Established Value R6 (VEVRX Quick QuoteVEVRX - Free Report) : 0.54% expense ratio and 0.45% management fee. VEVRX is a Mid Cap Value mutual funds that aims to target medium-sized companies that possess strong value and income opportunities for investors. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 10.78% over the last 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.