In terms of who is the biggest band in the world when comparing U2 and Coldplay, these numbers should bring everything back into focus:
U2 360 TOUR:
GROSS: $736,421,584 (RECORD)
ATTENDANCE: 7,272,046 (RECORD)
Average Gross: $6,694,742
Average Attendance: 66,110
Average Ticket Price: $101.27
Shows: 110
Sellouts: 110
COLDPLAY Mylo Xyloto Tour:
GROSS: $148,043,078
ATTENDANCE: 1,821,327
AVERAGE GROSS: $2,209,598
AVERAGE ATTENDANCE: 27,184
Average Ticket Price: $81.28
Shows: 67
Sellouts: 58
It should be noted that Coldplay still has 8 more shows to play on their current tour. There were also three shows not included in the above figures because they were not reported. In addition, one Coldplay show was cancelled, and 7 other stops on the tour were at festivals and not included in the above figures because they were not exclusive Coldplay shows.
Coldplay is indeed one of the most popular concert attractions around the world to come on to the concert scene since 1990. Despite that though, they are no where near U2 in terms of the concert drawing ability. In fact, in North America, they are still only about where U2 was on the Unforgettable Fire Tour back in 1985 after being in the business for 12 years.
Coldplay is indeed popular, but after five albums and 12 years in the business, they are no where near in a position to challenge U2 when it comes to concert popularity.