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.

Neuberger Berman Guardian Adviser (NBGUX Quick QuoteNBGUX - Free Report) has a 1.35% expense ratio and 0.9% management fee. NBGUX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. With yearly returns of 11.82% over the last five years, this fund clearly wins.

MFS Growth Fund R2 (MEGRX Quick QuoteMEGRX - Free Report) . Expense ratio: 1.13%. Management fee: 0.54%. MEGRX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. This fund has managed to produce a robust 16.03% over the last five years.

Van Eck International Investors Gold Y (INIYX Quick QuoteINIYX - Free Report) : 1.09% expense ratio and 0.73% management fee. Sector - Precious Metal funds like INIYX normally invest in stocks focused on the mining and production of precious metals such as gold, silver, platinum, and palladium. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 16.8% over the last five years.

So, there you have it - if your advisor has you invested in any of our "Magnificent Retirement Mutual Funds," they are certainly earning their keep. If not, you may want to look elsewhere.

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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.