It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.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.Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.Wells Fargo Large Cap Growth R6 (STFFX): 0.74% expense ratio and 0.68% management fee. STFFX 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. With annual returns of 11.06% over the last five years, this fund is a winner.Matthews China Small Companies Investor (MCSMX). Expense ratio: 1.43%. Management fee: 1%. MCSMX is a Pacific Rim - Equity fund, which usually invest in companies with a big presence in the export-focused markets of Hong Kong, Singapore, Taiwan, and Korea. This fund has managed to produce a robust 9.48% over the last five years.Ivy Mid Cap Growth A (WMGAX) is an attractive large-cap allocation. WMGAX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. WMGAX has an expense ratio of 1.12%, management fee of 0.77%, and annual returns of 13.5% over the past five years.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. Zacks Names "Single Best Pick to Double" From thousands of stocks, 5 Zacks experts each have chosen their favorite to skyrocket +100% or more in months to come. From those 5, Director of Research Sheraz Mian hand-picks one to have the most explosive upside of all. It’s a little-known chemical company that’s up 65% over last year, yet still dirt cheap. With unrelenting demand, soaring 2022 earnings estimates, and $1.5 billion for repurchasing shares, retail investors could jump in at any time. This company could rival or surpass other recent Zacks’ Stocks Set to Double like Boston Beer Company which shot up +143.0% in little more than 9 months and NVIDIA which boomed +175.9% in one year.Free: See Our Top Stock And 4 Runners UpWant the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Get Your Free (MCSMX): Fund Analysis Report Get Your Free (STFFX): Fund Analysis Report Get Your Free (WMGAX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research