Don't have their entire catalog of lp's, though have heard most of them and Achtung Baby is my favorite. Followed by Zooropa, believe it or not. Albums passed that point are not the same calibre imo, with the one exception being 'All that You Can't Leave Behind' which I like all the way through and think has some great songs on it.
From my experience most prefer the Joshua Tree, and that is certainly up there on the list for me as well, however a lot of their early stuff was too raw and flamboyant or something for me although on the other hand the enthusiasm of their youthful energy in that time period was also appealing in a way.
Being a big Daniel Lanois fan, I'm curious about Unforgettable Fire and would like to listen to in it's entirety at some point from beginning to end, even though I'm familiar w/ most of the tracks on the album.
Rattle & Hum is my other preferred U2 album, those 5 are basically my go to U2 albums, with the occasional song from elsewhere in their discography thrown in from time to time.
I recommend checking out this alternate rendition of 'Stay' by Craig Armstrong which Bono recorded a new vocal for.
https://www.youtube.com/watch?v=8CsHHhStENc
Bono & the Edge acoustic version of 'Stuck in a Moment' on Letterman Show.
https://www.youtube.com/watch?v=Xqrn2q3WCS8