Our "Magnificent Retirement Mutual Funds" list includes some of the best managed and best performing funds around. If you're already invested in these, congratulations! But if you're just now discovering them, don't worry. When it comes to your retirement, it's never too late to start investing in the best.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.Here are the funds that have achieved the #1 (Strong Buy) Zacks Rank and have low fees.Franklin Small-Mid Cap Growth R6 (FMGGX) has a 0.48% expense ratio and 0.46% management fee. FMGGX is a Small Cap Growth mutual fund building their portfolio around stocks with market caps under $2 billion and large growth opportunities. With yearly returns of 11.78% over the last five years, this fund clearly wins.Dreyfus/Boston Small/Mid-Cap Growth Y (DBMYX) is a stand out amongst its peers. DBMYX is a Mid Cap Growth mutual fund. Mid Cap Growth funds pick stocks--usually companies with a market cap between $2 billion and $10 billion--that demonstrate extensive growth opportunities for investors compared to their peers. With five-year annualized performance of 16.55%, expense ratio of 0.65% and management fee of 0.6%, this diversified fund is an attractive buy with a strong history of performance.Neuberger Berman Guardian Institutional (NGDLX): 0.7% expense ratio and 0.65% management fee. NGDLX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 12.55% 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 (DREVX): Fund Analysis Report Get Your Free (FMGGX): Fund Analysis Report Get Your Free (DBMYX): Fund Analysis Report Get Your Free (NGDLX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research