Welcome Julez!
My favourite U2 albums are as follows:
1. Achtung Baby - Also my favourite album of all time. This is simply a perfect combination of innovation and great songwriting. Each track offers something unique, the album flows seamlessly while each song still managing to offer something different from the last. If looking for awesome ballads, look no further than One or So Cruel. If looking for rock, then you don't get much better than Until The End Of The World or Even Better Than The Real Thing. The closing three tracks of the album are so underrated and are in my opinion three of U2's greatest ever songs and also three of the greatest songs of all time. Bono's vocals are terrific here, his voice isn't quite as good as in the mid to late 80's but the restraint he shows here combined with the wonderful falsetto is a joy to behold.
2. The Joshua Tree - What's there to say about this album? It is without a doubt one of the most wonderfully constructed albums of all time. No album flows better than this one and the feeling of being in a desert is captured so well, none mroe so than on the outstanding 'Running to Stand Still.' As well as obviously containing three classic tracks at the start of the album, there are plenty of underrated gems such as the aforementioned 'RTSS', 'Red Hill Mining Town' and the beautiful 'One Tree Hill.' Probably the best album for getting someone into the band.
3. The Unforgettable Fire - Rather underrated, definitely up there with their best work. 'Bad' is the best U2 track of all time, along with 'Stay', and only gets better live. 'A Sort of Homecoming' doesn't get the praise it deserves and would have been a killer single (I think I'm right in saying this wasn't a single? If not I stand corrected). 'The Unforgettable Fire' track is a soaring, melodic piece and contains some of Bono's greatest ever vocals. 'Promenade' is a hidden gem, a track I appreciate more and more after each listen. 'MLK' is a perfect way to close out the album. Could have moved into second place if not for the misstep which was 'Elvis Presley and America', and the fact that '4th of July' is essentially nothing but filler and means the album is only really 9 tracks long.
Honourable mention to Pop, which barely missed out on third place thanks to 'Miami', which is probably U2's worst song of all time. Apart from that the album is terrific, it is the most 'full' sounding album of theirs, after listening to it other albums in their discography can seem light in comparison. 'Discotheque' is a catchy enough song but a poor choice for a fist single, but the album is almost perfect from then on bar 'Miami' and 'The Playboy Mansion' (fun, silly song, but nothing too special).