If you're invested in any of the funds in our "Magnificent Retirement Mutual Funds" list, congratulations on owning some of the best managed and top-performing mutual funds. If you are lucky enough to discover our list of Top-Ranked Funds for the first time, it's never too late to start investing with the best, especially when it comes to your retirement.The easiest way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using our Zacks 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 highest Zacks Rank and the lowest fees.If you are looking to diversify your portfolio, consider AQR Large Cap Momentum Style N (AMONX). AMONX 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 0.65%, management fee of 0.25%, and a five-year annualized return track record of 10.37%.Principal Equity Income R5 (PEIQX). Expense ratio: 0.77%. Management fee: 0.51%. PEIQX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. This fund has managed to produce a robust 10.2% over the last five years.MassMutual Select Equity Opportunities I (MFVZX): 0.74% expense ratio and 0.69% management fee. MFVZX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 10.84% over the last 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.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 (AMONX): Fund Analysis Report Get Your Free (PEIQX): Fund Analysis Report Get Your Free (MFVZX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research