But seriously, folks, it's an interesting question made all the more so by the fact that both have one-person shows up at the moment. Gursky is razzle-dazzle, which isn't bad; Struth is a pondering philosopher, which is just as good. Both artists love drama: Gursky observes the world from a detached, God's-eye perspective; Struth is more the analytic inquisitor, a sort of explorer-wanderer. Gursky makes your heart beat faster; Struth makes your heart beat slower. Things get spooky when they engage in games of one-upmanship: Struth photographed a Pollock in 1994; Gursky shot the same one in '97. Struth made a Gursky-like crowd picture of the Chicago Board of Trade in 1990; Gursky shot there in 1997. Sometimes it feels like Gursky is stalking Struth.

Both artists have weaknesses: Gursky gets repetitive, and up close his images often break apart or grow cold; Struth can be solemn, starchy or pretentious. These days, Gursky is everybody's darling, the leader in the Struth, Gursky, (Thomas) Ruff race, an ongoing sideshow that is sometimes called Struffsky. (All are former students of the German Neo-Objectivists Bernd and Hilla Becher.)

Gursky specializes in flashy, panoramic images of edgeless postmodern life that reveal invisible structures of commerce, consumption and grandiosity. Although digital manipulation is often involved, Gursky's work is a form of high-style documentary. He's like a stunt photographer, a producer of special effects, or a maker of pattern-and-decoration photography. These pictures rarely tell you things you didn't know, and they don't add up to much, but it doesn't matter because he makes modern life look so cool, like a spectacular light show.

When Gursky is on, he's one of the few photographers that could make a moviemaker jealous. Here, the gigantic watercolor-like photograph of an L.A. supermarket is a spectacle of shelves, an indoor Grand Canyon of sugar, cola, mouthwash and deodorant. Or check out the commodity traders who morph into blasts of jubilant color. Then there is the picture of the Rhine, in which the silvery river turns into an ominous, synthetic strip of sea. When Gursky ventures from his formula, things go very wrong. In two works, he's trying to out-Struth Struth again, enlarging fragments of famous paintings to pointless, elephantine proportions. And in a truly vapid picture, he blows up a page of German writing.

Struth, meanwhile, is part über-poet Goethe, part hunter-photographer Hemingway. What Gursky is to spectacle, Struth is to the individual -- he's a searcher. While there are often people in their photographs, there is no one person in a Gursky: Everyone is a part in a machine. Struth is a humanist to the core. He has a relationship with the people he photographs, even if it's only abstract. He bemoans, almost broods over, the fact that "there is less and less space for the body." This guy is intense -- a soulful artist who is systematically exploring the different genres of photography (landscape, portraiture, interiors, still life and urban exteriors), often relating them directly to painting. Each series is distinct. Two are great; a few are clinkers.

The best is a group of huge color photographs of people looking at paintings in museums and churches. Through these very simple yet rich pictures, and more than any other contemporary photographer, Struth reveals the collective experience of seeing -- the joy, the weirdness and the wonder of looking at inanimate objects in public places. Gursky depicts people as a multitude; Struth shows them being human. In Struth's current exhibition, "New Pictures From Paradise," an interior of the Milan Cathedral is a showstopper. A religious service is in progress; parishioners pray, tourists with cameras look on, and paintings, gargantuan and magisterial, reign above. Photographed from some kinky isometric angle, space slides back and columns soar, while electric lights and stained glass illuminate this all-inclusive indoor universe.

At Goodman, 12 close-ups of dense, verdant forests show Struth once again on the move, this time investigating landscape photography. Each of these giant works is like one of the paintings in his museum photographs, and it's awesome to see so much nature in such fine detail and at such a luxurious scale. In two mossy Japanese forests, you don't know if you're looking at the real thing or a diorama. The Chinese jungle is a tracery of dappled green, and one from Australia looks like Rousseau's nude in the jungle without the nude. It would be hard to wear out these complex and striking photographs one at a time; together, however, they seem too much of one thing, and lose tension. They verge on National Geographic pics for the privileged.

Struth has been in transition for a couple of years, and here he still seems to be looking for something. When he's searching, he gets Byronic and slightly heavy. This may be because photography is such a total vision for him; he can't lighten up, play around, or jolt us like Gursky. When Struth is in probe-mode, as he is here, he plods -- ambitiously and gorgeously, perhaps -- but short of the standards he has set for his quest.