I wish there were a single place where everyone's money could earn ideal returns. Alas, we're all in different situations and phases of our lives, and what's best for me might not work for you. Still, I think I can suggest some investments that will appeal to a wide range of readers.

If you're young or patient ...
For Fools with a long investing time horizon, I'd recommend keeping much of your money in stocks, as opposed to bonds. According to research from business professor Jeremy Siegel, stocks have outperformed bonds 74% of the time over all five-year periods between 1871 and 2001. Over all 10-year periods in the same span, that figure rises to 82%. Meanwhile, stocks outperform bonds 95% of the time over all 20-year periods, and 99% of the time over all 30-year periods!

If you can't be bothered ...
If the idea of tending to your finances makes your head hurt and your eyes glaze over, I've got an investment for you: a simple index fund that tracks the performance of the overall stock market. Money plunked into the Vanguard S&P 500 Index Fund, or in its exchange-traded fund (ETF) cousin, S&P Depositary Receipts, also known as SPDRs, will instantly be invested in 500 of America's biggest companies, such as General Electric (NYSE: GE), Hewlett-Packard (NYSE: HPQ), and AT&T (NYSE: T).

The stock market -- which the S&P 500 roughly tracks -- has advanced, on average, some 10% per year over the long haul. If this pace keeps up, it will be enough to turn $10,000 into nearly $70,000 in 20 years, nearly $110,000 in 25 years, and nearly $175,000 in 30 years. Not bad, eh?

You can also invest in even broader indexes, such as the Dow Jones Wilshire 5000, which includes almost every public company, including those not in the S&P 500, such as Genentech (NYSE: DNA), Netflix (Nasdaq: NFLX), and Transocean (NYSE: RIG).

If you can be bothered a little ...
If you can handle doing a little legwork for your investments, you can aim to top the market's 10% average return. My personal recommendation here is mutual funds, in which I've increasingly invested lately. Once you identify some extremely promising funds, you can sock your money in them, then let their managers do the rest of the work. They'll find undervalued, growing companies, and decide for you when to buy into and sell out of them. The Janus Contrarian (JSVAX) fund, for example, has racked up average annual gains of more than 25% over the past five years and was recently invested in Amgen and J.C. Penney (NYSE: JCP).

When you look for top-notch funds, try to read up on fund managers, seeking those whose philosophies and styles appeal to you. Look for low fees, a lack of sales loads, reasonable turnover, and strong multiyear track records. I've found some very promising funds for my own portfolio via our Motley Fool Champion Funds investing service. (Its recommendations are beating the market 28% vs. 10%.)

If you're no longer a spring chicken ...
Of course, if you don't have your 40s, 50s, or 60s ahead of you, you might want to invest a little differently than younger investors. As you approach and enter retirement, it can make sense to pare your stock investments at least a little bit, replacing them with less volatile options such as bonds and money market funds.

Every investor should consider keeping a significant chunk of money in stocks. Why? Well, even if you're 60, you may well have another 35 years of life ahead of you. In other words, there's still plenty of time for stocks to perform on your behalf.

And if you're looking to perfect a conservative portfolio, we may be able to help. A free trial of Champion Funds will let you take a look at a variety of model portfolios. You can copy one exactly or mix and match the recommendations to suit your needs.

Here's to a happier portfolio!

This article was originally published on Dec. 4, 2006. It has been updated.

Longtime Fool contributor Selena Maranjian owns shares of an S&P 500 index fund. Netflix is a Motley Fool Stock Advisor recommendation. The Motley Fool owns shares of SPDRs. The Motley Fool is Fools writing for Fools.