There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

The easiest way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund 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 take a look at some of our top-ranked mutual funds with the lowest fees.

BlackRock Advantage Large Cap Value A (MDLVX Quick QuoteMDLVX - Free Report) has a 0.79% expense ratio and 0.49% management fee. MDLVX 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. With yearly returns of 12.69% over the last five years, this fund clearly wins.

Natixis Vaughan Nelson Mid Cap N (VNVNX). Expense ratio: 0.85%. Management fee: 0.75%. VNVNX is a Mid Cap Value fund, which usually invests in companies with a stock market valuation between $2 billion and $10 billion This fund has managed to produce a robust 12.41% over the last five years.

Thornburg Global Opportunities A (THOAX): 1.29% expense ratio and 0.83% management fee. THOAX is a Global - Equity mutual fund. These funds invest in large markets like the U.S., Europe, and Japan, and operate with very few geographical limitations With a five-year annual return of 14.71%, this fund is a well-diversified fund with a long track record of success.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.