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.

Brandes International Equity Fund I (BIIEX): 0.85% expense ratio and 0.75% management fee. BIIEX 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. BIIEX has achieved five-year annual returns of an astounding 16.26%.

Bridgeway Omni Small Cap Value Fund (BOSVX): 0.47% expense ratio and 0.45% management fee. BOSVX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. BOSVX, with annual returns of 14.09% over the last five years, is a well-diversified fund with a long track record of success.

Artisan Global Value Institutional (APHGX Quick QuoteAPHGX - Free Report) : 1.01% expense ratio and 0.99% management fee. APHGX is a Global - Equity mutual fund investing in bigger markets like the U.S., Europe, and Japan; these kinds of funds aren't limited by geography. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 14.41% over the last five years.

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.