drugstore.com, aided by top scores in customer service and cost, remains No.1 in the latest PowerRankings of online health retailers by Forrester Research, Inc. (Nasdaq: FORR). Forrester’s PowerRankings combines survey data from online consumers and unbiased shopping tests to provide objective rankings of the leading US eCommerce sites. The companies that rank below drugstore.com are PlanetRx.com, VitaminShoppe.com, and WebRx.com.

In a two-horse race, drugstore.com beats back a challenge from PlanetRX.com to win the health category for the second time in a row. drugstore.com’s victory was aided by high marks in customer service, cost, and shopper-friendly features, such as customer reviews and the ability to cancel unshipped orders online. But the site still has some rough edges. For example, its express checkout process is confusing, and the site charges customers a fee to order out-of-stock items.

Runner-up PlanetRx.com sports the best site performance and the quickest customer service replies. Additional positives include online order tracking, but the site lacks express checkout, customer reviews, and a 24-hour call center.

VitaminShoppe.com winds up a distant third due to low scores across the board. The site’s consistent navigation is a plus, but even loyal customers spend as much time checking out as first-time buyers. WebRx.com — a combination of three health sites — needs to work out the kinks in the new site, such as forcing shoppers to double-check zip codes and deleting different product types from the cart in different ways.

“drugstore.com manages to stay just ahead of a hard-charging PlanetRX.com, while the rest of the field lags far behind,” said Tom Rhinelander, senior analyst at Forrester Research. “Slow checkout and inconsistent customer service did in VitaminShoppe.com, while WebRx.com no doubt is struggling as it tries to integrate a host of sites including more.com, vitamins.com, and HealthCentralRx.com.”

For the latest PowerRankings, Forrester surveyed 20,000 consumers from the NPD Group’s online panel. These consumers identified the eCommerce sites that they purchased from most recently and rated their experiences. A team of Forrester shoppers then evaluated the shopping experience on sites that have a statistically valid number of consumer respondents by performing a series of rigorous tests. The consumer data and Forrester shopper scores were then synthesized and weighted, with consumer views accounting for two-thirds of the overall PowerRankings. A complete set of PowerRankings results — both consumer and Forrester shopper data — is made available to all ranked companies free of charge.

In the coming weeks, Forrester will announce the results of additional PowerRankings categories. Additional information about each of the categories, including a complete set of rankings and scores, can be found can be found at the PowerRankings Web site — powerrankings.forrester.com.