(MONEY Magazine) – With the onset of summer, millions of people will soon be gassing up their cars and driving hither and thither on America's roadways. And since you can't get from hither to thither without a good map, many of these travelers will be bringing along a road atlas. But which one should they use?

For years, that was a moot question. Rand McNally, which published its first road atlas in 1924, had the market largely to itself for decades. But the field is more crowded now: AAA, which has made maps for its members since 1911, got into the atlas game in 1985; National Geographic, long renowned for its reference maps, published an innovative new road atlas last fall; and Rand McNally, clearly aware of its competition, has just responded with a "Deluxe Edition" of its standard atlas, which echoes many of National Geographic's features. These publications offer essentially equivalent coverage of all the basic elements you'd expect from an atlas: major highways, cities, large towns, parks, scenic byways and so on. The distinctions among them, therefore, lie in their attention to small details, ease of use and compatibility with your personal travel style.

That last factor, of course, is quite subjective. Everyone has different travel habits, and a given atlas will necessarily cater to some better than others. Let's take a simple case study: me. Unless I need to get someplace in a hurry, I'll always take a local road over a high-speed freeway; I love driving through small rural towns; I rarely have a set itinerary, preferring to roam and to make decisions based on spontaneous whims; and I like travel to teach me things, preferably things I didn't even realize I wanted to learn. So I want an atlas that gives me easy access to as many small, quirky details as possible. With those biases in mind, here's how the atlases shape up.

Let's start with physical practicalities. If you have ever had the cover tear off a Rand McNally or AAA atlas or had the center map pages break free from the staples or simply had trouble wrestling with these oversize publications within the cramped confines of a passenger seat, you'll be glad to learn that the National Geographic atlas employs a high-quality spiral binding. This necessitates an irksome gutter of white space at the center of each two-page spread and also makes for a higher retail price ($14.95, compared with $9.95 for the staple-bound AAA and standard Rand McNally products). But it's not a bad trade-off--the covers and pages stay put, and the atlas lies flat, which makes it much easier to handle in tight quarters. The Rand McNally folks apparently liked this feature so much that they used the same thing for their Deluxe Edition (also $14.95).

Despite such an improvement, unfortunately, the spiral-bound products (as well as the standard Rand McNally) all have one immensely impractical feature: Their state-by-state indexes of towns and cities are all lumped together in the back of the atlas. Only AAA prints a state's index on the same page as the state map itself, which I find vastly preferable. If I'm driving through, say, Wisconsin, and want to visit the House on the Rock in Spring Green, the Mustard Museum in Mount Horeb and the Freshwater Fishing Hall of Fame in Hayward, I want to be able to find those towns on the map without constantly flipping to the index. And while all the atlases list the population of their indexed places, what good is this information when it's buried? If I stumble across an offbeat little town, I want to be able to look up its population without having to turn a few dozen pages.

Spokesmen for Rand McNally and National Geographic argue that printing the indexes on their map pages would eat up too much space. But a close examination proves otherwise. In fact, while the atlases all have essentially the same page size (roughly 11 inches by 15 inches), AAA's index-inclusive pages consistently offer the most generous map scale. Of the 42 states in which one atlas' scale is clearly superior to the others, AAA wins on 27 occasions. This is partly because AAA prints virtually each map on a two-page spread, while the other atlases relegate certain states--Idaho, Wyoming and West Virginia, for example--to a single page.

The roomier scale allows AAA to pack its maps with extra information, including more small local roads (other publishers deny this, but a close comparison plainly illustrates the difference), more cities and towns (about 60,000; the others have about 20,000), and interesting historical nuggets like ghost towns and the Oregon Trail.

The other atlases do have their strengths--the two Rand McNallys, for example, feature an extremely useful intrastate mileage chart accompanying every map. And National Geographic has upped the ante on a number of levels by incorporating more city inset maps, excellent depiction of topographic detail, a bookmark flap extending from the back cover and a contemporary color palette that makes its maps much more vivid (all copied, in varying degrees, by Rand McNally Deluxe).

But AAA is a drivers' organization, and this is reflected again and again in its atlas' attention to small but crucial details: Exit numbers on major highways are more prominently marked; county seats are easier to identify--no trifling matter if you're tooling around in the middle of nowhere and need to know where you're most likely to find a motel or a doctor; separate designations are used for dirt and gravel roads (the others simply list all such routes as "unpaved," but there's a big difference between the two, especially if it's raining).

While I prefer AAA, any of these products is a worthwhile travel aid. And for those who understand that the best part of a road vacation is the time spent just aimlessly rambling, the atlases all perform equally well when carelessly flung onto the back seat.

Paul Lukas is the author of Inconspicuous Consumption (Crown).