Ever since the Edge grew bald (probably in the Joshua Tree era, correct me if i'm wrong) he's been wearing different kinds of hats for each album era. During the Joshua Tree/Rattle and Hum era he wore that rain hat, during Achtung Baby/Zooropa he wore a bandana (he shoulda worn the bandana during the ZOOTV tour too cause he wore a beanie that time), during the Pop era he wore a cowboy hat and during the ATYCLB era he wore the beanie. I think he looked the best during ATYCLB. But he has a new look for every album so I guess no hats will be his look for the new album/tour.