Joshua tree is great, but just too normal. achtung is rock and roll like never done before, and it has yet to be matched.
I really couldnt chose between Joshua Tree and Achtung Baby , shit chuck in Rattle and Hum and there is A Trifecta of 3 amazing albums there , U2 at there finest across those 3 albums combined.
And to be honest I dont think I could ever chose just 1 album , way to hard.