Most health insurance will suit you just fine--until you get sick and really need it. When health plans are put under the microscope, the complaints from consumers begin to pile up.

That is a key finding from a new Consumer Reports National Research Center survey that studied the experiences of more than 37,000 readers in health maintenance organizations (HMOs) and preferred provider organizations (PPOs). The survey found that among readers who were not seriously ill, complaints about gaining access to care at an HMO or PPO typically hovered in the single digits. But the complaints were nearly three times greater for those with a serious illness.

Readers' experiences were far worse if they were in HMOs that ranked toward the bottom in satisfaction. Overall, 9 percent said they had trouble getting care, but complaints grew to 21 percent in the lower-rated HMOs combined for those who were seriously ill. Even the best HMOs saw a spike in complaints.

With the approach of the annual open-enrollment period, when millions of people who obtain health-care insurance through their employer or through Medicare will have the chance to switch plans, our Ratings will help you find HMO or PPO coverage that might provide better care.

It's an option many people might want to exercise, our survey found. One out of five people were sufficiently disappointed with their health-insurance plans that they wanted to switch to a new one, according to the responses we received. The major complaints included choice of doctors, billing issues, high out-of-pocket costs, and access to care.

We found that people enrolled in the lowest-rated HMO or PPO plans in our Ratings were twice as likely to want to switch out of their current plans as people in the top-rated HMOs and PPOs.

Other research has found enormous differences in the level of care different plans provide, with patients in the best plans more likely to receive the kind of high-quality care that translates into better overall health. One report found that if all health plans, HMO or PPO, provided the same disease-prevention programs, wellness plans, and best-practice treatments as the country's top 10 percent of health plans, as many as 81,000 deaths could be avoided each year. Up to $3.6 billion in unnecessary hospitalization expenses also would be saved, according to the 2006 State of Health Care Quality report issued by the National Committee for Quality Assurance (NCQA), a nonprofit health-care research group.

To discern the best plans, every two years we ask our readers to rate their HMOs and PPOs. This year we present detailed information on 34 HMOs, plans that pay almost all expenses for patients who stick to providers within a network, and 46 PPOs, plans that cost more but allow more choice of doctors. These health plans are among the top 100 in the country in number of people covered.

Only 67 percent of our readers said they were completely or very satisfied with their plan; that's up slightly from our total in our 2004 survey of HMOs and PPOs (64 percent). That rate is only average compared with what we've found when we've done consumer satisfaction surveys of other services.

For example, 84 percent of people who had an auto insurance claim told us in a 2004 Consumer Reports survey that they were either completely or very satisfied with their plan's service.

Why isn't satisfaction with HMOs and PPOs higher? Problems getting an appointment to see a doctor were reported by 10 percent of our readers, 21 percent had to deal with billing errors, 25 percent said they had a problem with their primary care provider, and 36 percent who called a plan representative for assistance said they had trouble getting the help they needed.

Many of the HMOs and PPOs whose plans we rated in 2004 earned similar scores in 2006, with a few notable exceptions. For example, Tufts Health Plan jumped to the top of our HMO list, improving six points from last time. Tufts has expanded the number of doctors in its plan, earning it a higher score in the choice of providers and access to care.

More respondents in HMOs complained they had to wait a long time to get appointments with doctors (14 percent vs. 8 percent in PPOs). If you were not in one of the top-rated plans in our Ratings, getting access to needed care was much tougher especially for the seriously ill. Although HMOs have traditionally limited the pool of doctors participants could use, and sometimes require referrals to specialists, people in HMOs were as satisfied with their choice of providers as people who were in PPOs.

"Many HMOs have developed a product that allows members to receive treatment from doctors outside the network," says Gary Claxton, a Kaiser Family Foundation vice president and co-author of the Employer Health Benefits survey. "It may or may not be called an HMO. And most HMOs have made an effort to expand the number of doctors in their networks." (The Kaiser Family Foundation is not related to the Kaiser Permanente health plan.)

PPOs have their limitations as well. Members of PPOs not only have to pay more for their coverage, they also report more difficulty receiving the reimbursements they're owed. Among those who contacted their health plan, 62 percent in PPOs said it was due to a problem they had with a bill or claim, compared with only 30 percent of HMO members. And our HMOs vs. PPOs comparison found that PPO enrollees also experienced more difficulties with customer support, complaining that they had to phone or write the plan several times and that solving the problem took an unreasonable amount of time. And 32 percent of seriously ill PPO members said they had billing hassles versus only 13 percent of HMO participants.