The stock market is like an unreliable friend.

Even if he's affable and generous this year, you're wary of his companionship if he squandered most of your money last year.

Market volatility has a number of investors questioning just how much more excitement they can accept from their personal portfolios. The stock market comeback has been well and good, but it can't erase the memories of earlier heartache.

"Right now a lot of folks feel they'd have a hard time accepting the same kind of experience they had with equities in 2008," says Marilyn Capelli Dimitroff, certified financial planner and president of Capelli Financial Services Inc., in Bloomfield Hills, Mich. "They came to understand just how volatile stocks can be."

The basic mid-range formula for personal portfolios traditionally has been 60 percent stocks and 40 percent bonds, based on a belief that provides the ability to keep up with inflation with some cushion as well. Percentages are adjusted according to an individual's risk preference, the types of stocks and bonds, and the investment time frame.

The question is whether the trauma of last year dictates that stock percentage should shrink or disappear—just to be on the safe side. Most financial experts contend that tossing out stocks would be a huge mistake.

"While we've had a wake-up call, nothing has changed because a solid strategy takes into account all possibilities of market performance, including bubbles and crashes, since that's what happens in stock markets," says Tom Jacobs, co-founder and portfolio manager for Complete Growth Investor, of Marfa, Texas. "In fact, after a crash like we had it's more important to stay the course, because we're even less likely to have something of that magnitude again."

Tradition dictates that the younger the investor, the higher the stock percentage, with that percentage declining as more money is switched into bonds on the way to retirement. But that belief has lost some steam.

"Age is probably the least relevant factor in considering how much an individual should have in stocks," says Harold Evensky, certified financial planner and president of Evensky & Katz, of Coral Gables, Fla. "Even someone 65 years old could have another 20 years to go."

Two 65-year-old couples might have the same size portfolios but completely different allocations based on whether they have pensions, how much they spend, and their risk tolerance, he says.

"To base everything in a portfolio on a person's age is just ridiculous," says Dimitroff, who agrees that overall situations matter more than age. "Older people have a shorter time for their portfolios to recover, but young people have such high cash needs that a higher equity allocation might not be so smart for them."

There is danger in believing a strong shift into bonds means you're absolutely safe, warns Dimitroff. Bonds can have considerable risk, especially when you're starting with historically low interest rates and increased inflation could be ahead. For existing 30-year bonds, a 1 percent rise in interest rates could lower their value by as much as 15 percent, she says.

In addition, high-yield bonds perform more like stocks than bonds, Dimitroff says, and are quite different from traditional corporate bonds, municipals, or treasury notes.

"Our basic belief is the domestic and world economies will continue to grow, and stocks will earn more than bonds," says Evensky. "You need to start with a philosophy or belief, but if you need a 5 percent real rate of return, you're not going to get it in bonds and will in stocks."

The stock portion could be stocks, stock mutual funds, or exchange-traded funds. Evensky admires ETFs because they are cost-efficient and tax-efficient, which makes a big difference in long-term results. The bulk of your money for stocks should be used to buy the stock market as cheaply and tax-efficiently as you can, he says.

Some examples of inexpensive basic ETFs worth considering are:

•SPDRS (SPY) that tracks the popular Standard & Poor's 500, a diversified large- and mid-cap index of U.S. companies on major U.S. stock exchanges. It is the oldest and most actively traded ETF by dollar volume, and its 0.09 percent expense ratio is one of the cheapest.

•iShares Russell 3000 Index (IWV), which tracks the 3,000 largest companies in the U.S. by market capitalization, represents about 98 percent of the total U.S. stock market.

Its 0.20 percent expense ratio is lower than even most index mutual funds.

Within the stock portion of an individual's portfolio should be some "defensive value" stocks, advised Jacobs. In that group he'd include stocks such as ConocoPhillips (COP) because it is the largest natural gas producer in the U.S. and ExxonMobil Corp. (XOM) because it has the largest energy reserves and a pristine balance sheet.

He'd also include Johnson & Johnson (JNJ) because it will always be "moving its money around" effectively between health care and consumer drugs and PepsiCo Inc. (PEP) because its diversification beyond beverages into snack foods gives full exposure to the consumer.

"You're not going to light the world on fire with these names, but you're not going to get hurt either," says Jacobs.