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.If you are looking to diversify your portfolio, consider Direxion Monthly S&P 500 Bull 2X Investor (DXSLX). DXSLX is an Allocation Balanced mutual fund. Allocation Balanced funds look to invest across asset types, like stocks, bonds, and cash, and including precious metals or commodities is not unusual; these funds are mostly categorized by their respective asset allocation. This fund is a winner, boasting an expense ratio of 1.32%, management fee of 0.75%, and a five-year annualized return track record of 18.87%.Fidelity Fund (FFIDX) is a stand out amongst its peers. FFIDX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset. With five-year annualized performance of 13.94%, expense ratio of 0.45% and management fee of 0.32%, this diversified fund is an attractive buy with a strong history of performance.AllianzGI Convertible Fund Admiral (ANNAX). Expense ratio: 0.93%. Management fee: 0.57%. Five year annual return: 13.01%. ANNAX is a Convertible Bonds mutual fund, and these funds are unique in the fixed income world; these securities have components of both fixed income and equity, making them hybrid securities.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. 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 Up >>Want 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 (ANNAX): Fund Analysis Report Get Your Free (DXSLX): Fund Analysis Report Get Your Free (FFIDX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research