The funds in our "Magnificent Retirement Mutual Funds" list are among the best managed and best performing mutual funds available. If you are just finding out about our Top-Ranked Funds list, we welcome you!How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using our Zacks Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.Let's break down some of the mutual funds with the highest Zacks Rank and the lowest fees.If you are looking to diversify your portfolio, consider Janus Henderson Global Technology A (JATAX). JATAX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. This fund is a winner, boasting an expense ratio of 1.01%, management fee of 0.64%, and a five-year annualized return track record of 18.74%.Davenport Small Cap Focus Fund (DSCPX) is a stand out amongst its peers. DSCPX is a Small Cap Blend mutual fund that usually targets companies with a market capitalization of less than $2 billion. With five-year annualized performance of 10.67%, expense ratio of 0.96% and management fee of 0.75%, this diversified fund is an attractive buy with a strong history of performance.MFS Mass Investors Growth Stock C (MIGDX): 1.47% expense ratio and 0.33% management fee. MIGDX 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 a five-year annual return of 13.14%, this fund is a well-diversified fund with a long track record of success.There you have it. If your financial advisor had you put your money into any of our "Magnificent Retirement Mutual Funds," then they've got you covered. If not, you may need to talk.Do You Know the Top 9 Retirement Investing Mistakes?Investing in underperforming mutual funds is just one of the key errors that can derail your retirement plans.To learn more, read our just-released report: 9 Retirement Mistakes You Need to Avoid.This report can help you sidestep these costly mistakes and potentially achieve your retirement goals. Get Your FREE Guide Now Get Your Free (DSCPX): Fund Analysis Report Get Your Free (JATAX): Fund Analysis Report Get Your Free (MIGDX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research