March is almost behind us, and good riddance, too. Yesterday offered a modest reprieve, but Vanguard 500 Index (FUND:VFINX), the venerable S&P tracker, has shed more than 3.3% of its value thus far during the month, while Cubes, the popular Nasdaq 100 tracker (NASDAQ:QQQQ), has declined by 3.4%. And woe, too, unto Diamonds (AMEX:DIA) investors. This exchange-traded fund (ETF) tracks the bluest of blue-chip indexes -- the Dow Jones Industrial Average -- and since March darkened our doorsteps, that particular bogey is also off more than 3%. Yikes. Talk about diamonds in the rough.

For long-term investors, however, now -- as with every market dip -- looks like an interesting buying opportunity. To be sure, you have to pick the right investments -- and that's precisely what my Champion Funds newsletter service is all about. But if you're going to be in the market for the next 10, 15, or even 20 years, why not take advantage of Mr. Market's periodic mood swings?

Worry warts
To be sure, there's never a guarantee that the market won't decline further. Market mavens are generally nervous nellies, and these days, their worries du jour come in triplicate: the sky's-the-limit price of oil; Alan Greenspan's inflation jitters; and those big -- and ever-growing -- concerns about the size of the U.S. budget deficit. And heck, if we really want to wring our hands, let's go ahead and throw in the soft dollar for bad economic measure.

Far be it from me to cast aspersions on the worry warts, but I generally think the time to invest for the long haul is just about always right now. Over time, the market has appreciated to the tune of roughly 10.5% annually, and I'm thoroughly convinced that a well-chosen basket of mutual funds can leave that mark in the dust.

But what, exactly, constitutes "well-chosen"? Good question.

Greatest hits?
The perfect portfolio, of course, is always a work-in-progress, something that you'll tweak and adjust as your timeline and tolerance for volatility changes. That said, any investor needs a starting point, and for those with a long-term outlook -- not to mention plenty of patience for the market's inevitable ups and downs -- the Aggressive model portfolio that we just rolled out in Champion Funds makes a rock-solid starting point. Among other things, it's a portfolio anchored by superior funds that count the likes of Research In Motion (NASDAQ:RIMM), Genentech (NYSE:DNA), SBCCommunications (NYSE:SBC), and Target (NYSE:TGT) among their top holdings.

And as I pointed out in detail in my previous commentary, our Aggressive portfolio picks have it all over the typical mutual fund, scoring major points in such key areas as manager tenure, fees, and, of course, performance.

The portfolio itself is just a free trial away, and it if suits you, wonderful. Even it doesn't, however, our model still provides a high-quality yardstick, a benchmark you can use to gauge the portfolio you may have haphazardly assembled in your IRA or 401(k) plan, or perhaps even the one that resides in your taxable investment account -- you know, the one that looks more like a greatest hits collection than a full (and wholly satisfying) album.

Intelligent asset allocation
The point is, intelligent asset allocation matters -- and it matters a lot. And for those of you who are nearing (or are perhaps already in) retirement, not to worry: Champion Funds will soon roll out model portfolios with your needs in mind, too. Indeed, those will hit the streets in April and May, respectively.

In the meantime, I encourage all investors with funds in their portfolio -- and I have a hunch that that includes you, Fool -- to take a close look at their holdings and ask themselves this not-so-musical question: Is this really where I want to be, investment-wise?

Not to be a naysayer or anything, but my guess is that it's probably not -- and I speak from experience. When you're given 15 minutes and a form to fill out, it's pretty darn easy to make the wrong 401(k) choices, after all. And even after you've had some time to think about it, it's all too easy to chase yesterday's winners instead of tomorrow's winners today.

That's an honest investment mistake that just about anyone can make. But you don't have to make it. Indeed, that's a central part of the Champion Funds premise. Yes, the fund universe is full of duds. But with a smart asset allocation model as your guide -- not to mention a cherry-picked collection of funds to choose from -- you're going to have a tough time going wrong.

Shannon Zimmerman, chief analyst for Motley Fool Champion Funds, knows when to fold 'em and when to hold 'em. Click here for a free test drive of hisnewsletter service. Shannon doesn't own any of the securities mentioned. The Motley Fool is investors writing for investors.