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.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

Alger Growth & Income Fund A (ALBAX Quick QuoteALBAX - Free Report) has a 0.92% expense ratio and 0.5% management fee. ALBAX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. With yearly returns of 13.37% over the last five years, this fund clearly wins.

Fidelity Value Fund (FDVLX): 0.69% expense ratio and 0.67% management fee. FDVLX is a Mid Cap Value mutual fund, which targets medium-sized companies with a market cap between $2 billion and $10 billion. With yearly returns of 11.96% over the last five years, FDVLX is an effectively diversified fund with a long reputation of solidly positive performance.

FPA Queens Road SmCap Value Ins (QRSIX). Expense ratio: 0.79%. Management fee: 0.66%. Five year annual return: 11.41%. QRSIX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion.

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.