Here's a look at the Internet's biggest shopping malls. At each mall, we hunted for the same portable CD player: Aiwa's Cross-Trainer XPSP-90.

1. Yahoo Shopping. Yahoo rents space to more than 7,500 retailers and creates a unified way for shoppers to shop from different merchants. You can browse by store name or product category, or type a product name into the search box to see various stores' prices. Our search revealed four listings, at prices ranging from $99.95 to $101. Shoppers who are stumped can click on "what other shoppers are buying" and see a sample of what sold in the past hour. Yahoo's express checkout and "wallet" system will remember your shipping and credit card data and transmit it to each merchant automatically. But the checkout system requires separate "shopping carts" for each merchant--at least they're all on one page.

2. Shop at AOL. Shop at AOL is the simplest online mall to use. With 275 merchants, it has far fewer stores than Yahoo; AOL prefers to focus on well-known retailers. Like Yahoo, AOL offers a digital wallet with a quick-checkout feature accepted by most merchants. Shop at AOL's pull-down menu bar travels with each shopper from merchant to merchant, making it easy to stay within AOL's shopping partners even though all of their stores are outside AOL's proprietary area. AOL also uses several dozen gift catalogues to showcase products. Its new search system lets shoppers refine searches by selecting favored retailers, but there's no search box on the home page--we had to drill down to "electronics" to run our query, which found the CD player selling for $87.99 (but the link for it only took us to the merchant's home page, requiring further mousing around to find the item itself). Frustrated shoppers should be able to get a live customer service agent on the phone or by using AOL's instant-messaging system.

3. AltaVista/Shopping.com. AltaVista launched a shopping service last month with a limited number of merchants but a well-organized guide and a powerful price-comparison tool, plus product reviews and recommendations from fellow shoppers. It lets shoppers look for items not only on AltaVista's own Shopping.com superstore, but also from merchants that rent space in this mall. Our search first found us a photo and description of the CD player; clicking on "find a merchant" found it on sale for $99 and $119 at different stores.

4. MSN eShop. Microsoft Corp.'s redesigned mall features 60 merchants, including well-known retailers, and offers gift recommendations and other help for confused customers. Biggest quibble: MSN offers no search box, forcing shoppers to browse by category. By doing so, we found the Aiwa CD player on sale for $87.99. EShop is rolling out an ambitious tool to help compare merchandise by price, brand and other features across many merchants, but this complex mechanism may be too difficult for many users. The site's new Zip-code store locator, which finds physical-world stores near you, still omits many stores.

5. Lycos Shop. The Lycos mall has a unified checkout system across hundreds of merchants, but it's poorly organized: Retailers are hard to shop by name, and entering product names or categories in the search box produced confusing results. Three different queries for the CD player turned up nothing. Lycos, like Yahoo, offers a rewards program in which shoppers can accumulate points for each dollar they spend and redeem them on special products. It has an advanced (read: complex) comparison tool, which asks people questions about shopping priorities--how much they care about brand names or customer service, for instance--and then presents a "value" score for each product. We couldn't locate the Aiwa with this tool either.

6. Excite. Excite At Home's new mall, barely a week old, is one of the easiest to browse, if not to search; our test search produced a long list of hits, but only two correct matches for the Aiwa, at $87.99 and $99.70. Its express checkout system goes further than most malls by letting shoppers save items from different merchants in the same cart. But they still have to click from the shopping cart to make the purchase at each store, using a digital wallet system. Excite's 3-D holiday shop, which displays three-dimensional views of gifts, is useful only with a fast Internet connection.