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.Oppenheimer Discovery A (OPOCX): 1.08% expense ratio and 0.62% management fee. OPOCX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. OPOCX has achieved five-year annual returns of an astounding 11.64%.WCM Focused International Growth Fund Investor (WCMRX): 1.26% expense ratio and 0.85% management fee. WCMRX is a part of the Non US - Equity fund category, many of which will focus across all cap levels, and will typically allocate their investments between emerging and developed markets. WCMRX, with annual returns of 11.23% over the last five years, is a well-diversified fund with a long track record of success.Baird Midcap Investor (BMDSX) is an attractive large-cap allocation. BMDSX is a Mid Cap Growth mutual fund. These funds aim to target companies with a market capitalization between $2 billion and $10 billion that are also expected to exhibit more extensive growth opportunities for investors than their peers. BMDSX has an expense ratio of 1.07%, management fee of 0.75%, and annual returns of 11.27% over the past five years.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 (BMDSX): Fund Analysis Report Get Your Free (WCMRX): Fund Analysis Report Get Your Free (OPOCX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research