Nearly every traveler has at least one of ''The Big Three'' online booking agencies logged into their favorites list.

Each site accomplishes the basics -- booking flights, hotels, rental cars, cruises, vacation packages -- so which you use may be a matter of personal preference. But there are some differences between them. Here's a snapshot. (Information was supplied by the companies and augmented by our research):

EXPEDIA

Overview: Expedia has the most expansive online toolset and handles some less-common foreign routes (including flights within China, India and Africa). Some airfare and hotel deals are available only on Expedia. Deals are prominently displayed. Expedia also offers a no-blackout-dates rewards program. The appealing, easy-to-use home page and tools make this our favorite of the Big Three sites.

Founded: 1996

What it sells: Flights, hotels, rental cars, vacation packages, activities in your destination. Users can search the site by destination or interest (family, adventure, beach, romance, luxury, Walt Disney World, ski, golf/spa, all-inclusive).

Does not include: Some low-cost carriers such as Southwest and Easyjet

Booking fees: $5, in some cases free

Deals by e-mail: By free subscription.

Last-minute deals area: Yes

Fare alerts: Download a widget that alerts you when prices drop on a specified city pair. Drawback: Only specific U.S. airports are included.

Phone support: 800-EXPEDIA, open 24/7, with no additional booking fee. During regular U.S. business hours, staff typically is U.S. based but during other hours may be offshore. Doesn't reveal the number of phone staffers.

Price guarantee: Find a better price online for the same trip within 24 hours and Expedia will refund the difference plus a travel coupon for $50.

Flexible date searches: Yes, on major domestic routes. It also offers a ''flight fare'' calendar that helps you see cheapest times to fly.

Rewards program: Thank you points are awarded at 1 point per dollar spent and may be combined with other thank you points and awards through the Citibank network.

User-generated hotel reviews: By travelers who stayed at the hotel in the past six months.

Cool tools: Expedia's online toolset (Click See all tools under Plan Your Trip) includes airport guides (both MIA and FLL are included), alerts if your flight is delayed, driving directions/mapping, gas station finder (good for finding stations convenient to airports), group bookings for hotels and cruises, split payment (in case you and your companion are buying your air separately), limited seat alerts that let you know when an air fare is selling out, and a cruise calendar (alas, not very detailed).

Check out: Insider Selects, a ranking of the world's top hotels determined by a matrix based on consumer reviews, a value model and Expedia's experts. (The Ritz-Carlton on Key Biscayne ranks No. 4.)

ORBITZ

Overview: Orbitz specializes in domestic travel and foreign cities with travel originating in the U.S.; includes foreign hotels and car rental. The company prides itself on its customer care program, and consumer advocate/Travel Troubleshooter Christopher Elliott agrees that of the big travel web agents, Orbitz uses the combination of people and technology most effectively. The site caters to niche markets including family, ecotourism and gay-and-lesbian travel.

Founded: 2001