i luvvv achtung baby... then joshua tree... then war, my top three, with the unforgettable fire and how to dismantle (you heard me) close behind. most of my other choices are pickin and choosin tracks here or there. (for example, i adore the song 'stay' offa zooropa, but i could manage not much more than a meh for the rest of that album.)
i would call achtung baby and joshua tree outright masterpieces.
i think they're a polarizing band, probably becuz of some combination of (a) a very distinct sound that tends to win you or lose you; and (b) bono and his yap.
at their best? not only incredible music but inspired, poetic lyrics. achtung, coming when it did, as it did, ditching the successful formula, so to speak, and going for broke in breaking new ground... just phenomenal. and in my opinion, it all worked. i still spin that album regularly.