Who's the greatest, U2 or the Stones?

The Rolling Stones vs. U2. Mick vs. Bono. Keef vs. the Edge.

Who is the world's greatest rock 'n' roll band? Baby boomers might argue the Stones. Gen Xers might advocate for U2.

Last week, this baby boomer had the rare opportunity to see these iconic bands on back-to-back nights: the Stones on Tuesday in Milwaukee, U2 on Wednesday in Chicago.

How were the shows? Outstanding. Was one better? Yes. Which band was the greatest? I'll answer that later. First, impressions and experiences.

Just given their ages, the four Stones, 68 to 74, have to be in the autumn of their 53-year career. U2, a quartet ages 53 to 55, are in midcareer — year 39, to be exact — sort of like the Stones in the mid-1980s. U2 is coming off two slow-selling, hits-devoid albums, the latter of which, "Songs of Innocence," resulted in bad karma because it was sent for free last year to hundreds of millions of iTunes users, some of whom saw it as unwanted spam.

Songs from the new album, which was produced by trendy hitmakers including Danger Mouse and Ryan Tedder, are the focus of U2's current Innocence and Experience Tour. The Stones, by contrast, haven't released a studio album of new material since 2005 and their ZIP Code Tour is a corny euphemism for Just Another Greatest Hits Tour.

Although both bands are onstage for about 2 hours and 10 minutes, the shows are as different as Mick Jagger, the athletic businessman extraordinaire, and Bono, the stocky, soul-searching activist. The Stones were inspired by American blues, U2 by American idealism.

Sir Mick and the Stones just want to have fun — like a bunch of carefree but handsomely paid guys gigging in a rock club. Seeing them at the Marcus Amphitheater (the smallest venue on their stadium tour) was almost like seeing them in a large club. The stage was smaller than at Minneapolis' TCF Bank Stadium, the runway shorter. From the 13th row, I had little sense of the 25,000 people behind me.

The Stones were loose, mostly devoid of choreography though they had color-coordinated outfits (shades of green) for original members Jagger, Keith Richards and Charlie Watts. As he did in Minneapolis, Jagger made localized comments. "Hello, Cheeseheads," he declared to beer-boosted cheers.

When they're on, the Stones are a relentless rhythm machine, and they found their groove on "Sympathy for the Devil," "Brown Sugar," "Midnight Rambler" and the Lisa Fischer-fueled duet "Gimme Shelter." While Jagger was the consummate frontman full of practiced charm and ageless moves, Richards provided the key riffs on "Start Me Up" and "Satisfaction" that have helped define the Stones' sound.

The moment that may have illustrated the essence of the Rolling Stones was when opening act Buddy Guy, a 78-year-old blues legend, joined them for the blues chestnut "Champagne and Reefer." Completely unrehearsed with Jagger ordering solos on the fly, it was truly a case of veteran musicians creating music for the sheer joy of it.

While the Stones play rock 'n' roll, U2 performs rock as art. Their show at United Center (repeated Monday and Thursday; no Twin Cities dates) is meticulously staged, overwhelmingly purposeful and undeniably thrilling.

In his long-winded way, Bono talked about the idealism of his youth — the days of innocence — and how things have changed. He even portrayed his younger self confronting current Bono: "Who are you? Have you forgotten who you are?"

The Man for All Causes discussed the wars in Ireland and the significance of the idea that America stands for. Despite all Bono's pontificating, the sound of these four musicians was, at turns, throbbingly powerful, stripped-down gorgeous and elegantly crafted. While the new tunes had more impact and drama live than on disc, the high points were "Pride," "Where the Streets Have No Name" and other time-tested anthems.

What ultimately elevates the concert to greatness is the staging. The innovative presentation features two giant LED curtains hanging over a runway the length of the arena, with a catwalk between the video curtains creating a cool see-through effect of the musicians performing inside their larger projected images.

In an unexpected moment, Bono thanked Jagger for showing up at United Center — humbled and honored by being respected by one of his own heroes.

After the respective concerts, U2's crowd was definitely more abuzz than the Stones fans, who had dropped as much as $400 for 19 songs while the U2 faithful had paid up to $275 for 24 tunes.

Years ago when I asked Richards if the Stones were the world's greatest band, he said, "On any given night, any band can be the greatest rock 'n' roll band in the world. There's got to be 50 out there — at least — tonight. Everyone's up for the title."

Last week, the Stones were the greatest on Tuesday, but U2 was even greater on Wednesday.

Twitter: @JonBream • 612-673-1719