It has to be "War"..half of that album is pretty unlistenable for me, there are some really dodgy funk sounds and vocals on it, which is a shame since the other half of the album I find to be among U2's best.
I honestly think WAR sounds the most dated. More and more I'm starting to think that WAR is possibly the weakest U2 album. In fact in my opinion I'm pretty sure of it.
POP also has a dated feel to it because it's the first U2 album I ever bought and it, more than any U2 album takes me back to a certain time. More a fault of circumstances rather than album quality I suppose.
I think JT sounds the most dated. The band no longer look or sound like that. Some of the lyrics are no longer applicable as Bono wrote artistically but still specifically about issues (which contrasts an album like AB, where the lyrics are applicable to any time and any place). And while I adore songs like "Streets", "Exit" and "One Tree Hill", I feel the band have advanced so much that most of JT just sounds "old" to my ears. I feel that U2 challenged themselves more on other albums.
"October" is also another album that sounds very dated, but it's more because of U2's style and overall sound then. "Boy" still has a freshness to it - analogous to bands like BRMC or Franz Ferdinand. It doesn't have that 80's feel, which "October" does (at least to my ears).
To me, every U2 album except maybe OCTOBER could be released now and sell a lot! However, surprisingly, I think (like many of you) that WAR is the most dated..... I don't know why, I think it is also due to the sound, very 80's, Bono's voice is very special and not the same as now.... and some songs like The Refugee, Red Lights just don't sound fresh.
However, WAR is one of my favourite U2 album......
The least dated might be HTDAAB ..... but from the older ones, no doubt, ACHTUNG BABY is the freshest!!!! If it was release now it would sell as much as it did in 1991..... just so perfect!
I forgot R&H..... I think this is the most dated, I mean the studio songs like Angel of Harlem, Love Rescue Me, When love comes to Town....... no more, please no more!
I guess I'd say the only albums that haven't dated that well are UF and War, but there are songs on both of those albums that still sound pretty fresh.
For me all of them except for Bomb. But for me it is always like that. When they come out with a new CD I play the shit out of it untill the next one comes out.