Being the biggest band in the world is a tough job, which is why U2 have sloughed it off now and then: Periods of arena-scale romance have been followed by bursts of odder experimentation, including a less-than-stellar Nineties stretch when the band were mired in irony, postmodernism and orange goggles. But for much of their career, U2 have committed to grabbing and holding that Biggest Band title the way they commit to everything — completely and passionately.