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, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Oppenheimer Gold & Special Mineral Y (OGMYX Quick QuoteOGMYX - Free Report) : 0.82% expense ratio and 0.58% management fee. Sector - Precious Metal funds like OGMYX normally invest in stocks focused on the mining and production of precious metals such as gold, silver, platinum, and palladium. OGMYX has achieved five-year annual returns of an astounding 11.49%.

Brown Advisory Sustainable Growth I (BAFWX Quick QuoteBAFWX - Free Report) : 0.64% expense ratio and 0.53% management fee. BAFWX 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 13.63% over the last five years, BAFWX is an effectively diversified fund with a long reputation of solidly positive performance.

T. Rowe Price Cap Appreciation Adviser (PACLX Quick QuotePACLX - Free Report) . Expense ratio: 0.97%. Management fee: 0.58%. Five year annual return: 10.28%. PACLX, an All Cap Value option, is a type of mutual fund that buys stakes in companies in all three valuation categories.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.