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.

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 the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term investors' portfolios.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

Third Avenue Value Z (TAVZX) has a 1.06% expense ratio and 0.9% management fee. TAVZX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. With yearly returns of 14.79% over the last five years, this fund clearly wins.

Goldman Sachs Intl Eq Insights R6 (GCIUX Quick QuoteGCIUX - Free Report) : 0.78% expense ratio and 0.75% management fee. GCIUX is a Non US - Equity option, focusing their investments acoss emerging and developed markets, and can often extend across cap levels too. With yearly returns of 11.92% over the last five years, GCIUX is an effectively diversified fund with a long reputation of solidly positive performance.

Invesco Technology Fund A (ITYAX): 1% expense ratio and 0.6% management fee. ITYAX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. With a five-year annual return of 16.45%, 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.