Really, it depends on what you are looking to do. Are you looking to get heavy into trading or do you just want a few boots to listen to?
If you are looking to get into trading I wouldnt recommend going after the standard boots that are mentioned above or what I mention below. Most traders have those. B and P for some shows you dont see all over the place. You are more likely to find people to trade for those versus a copy of Chicago 87 Rocks Hottest Ticket boot, most traders have that.
If you are looking just for a few good boots then some of the suggestions above are good ones. Go for the setlist that looks good AND quality. Lets face it, if a recording is awful and you are not a completist its useless to get it as you will never listen to it. My suggestions quality wise are:
BOY
3-6-81 Boston FM recording, great show
October
11-13-81 Albany FM recording, good crowd and energy
WAR (take your pick here)
5-5-83 Boston soundboard perfect recording
5-30-83 Devore (US Festival) FM recording (my personal fav)
6-5-83 Red Rocks FM recording complete (for obvious reasons)
The Unforgettable Fire
10-23-84 Nantes soundboard, the only complete board of this tour circulating.
11-21-84 Dortmund FM broadcast, incomplete though
2-5-85 Bologna Great audience recording, crowd and show
3-21-85 Chicago Great audience recording
The Joshua Tree
4-29-87 Chicago Great audience recording, most people have this one
5-8-87 Hartford Very good audience recording, fantastic setlist, one of my favorites from the JT tour.
11-7-87 Denver Soundboard(video feed), get the Back In Denver boot of this one, its the best version.
Lovetown (one of my favorite tours)
11-18-89 Sydney Very good audience recording, rated as one of U2's best shows of any tour.
12-26,27, 30, 31-89 Dublin, as mentioned before, all are soundboards except 12-31 which is an FM broadcast. Everyone votes for 12-31 (New Years show) but I prefer 12-30, better setlist and from some friends that went to all 4 shows, they said this one was the best.
Zoo TV
4-21-92 Tacoma Excellent audience recording and show
6-11-92 Stockholm (as mentioned above) there is an audience and video feed version of this. I actually think the audience version is a tad better.
11-14-92 Houston Excellent audience recording
8-12-93 London Excellent audience recording (some good setlist changes, IE Zooropa and Babyface)
8-21-93 London Excellent audience
8-30-93 Dublin FM broadcast, most people have this one.
11-16-93 Adelaide Soundboard(video feed) more raw than Sydney, like this one a little better actually, more laid back.
11-27-93 Sydney FM broadcast (Get the Westwood One version, its the best and its all in stereo versus some other versions)
Popmart
12-3-97 Mexico City FM broadcast Most have this one
1-31-98 Sao Paolo FM broadcast, Edge indicated he thought this was the best shows of the tour.
2-11-98 Santiago FM broadcast, great show, great crowd.
Elevation
5-15-01 Chicago ALD, this recording is great IMO. Great show show and setlist.
5-16-01 Chicago just for the setlist
(I may be a bit bias though on Chicago as I was at those)
6-9-01 Boston great setlist
7-21-01 Turin longest show and setlist of the tour
10-10-01 South Bend (direct satellite feed) fantastic quality, good show (get this one over the webcast versions, its way better)
(See Chicago above, I was at this one also, so I may be bias, LOL)
10-31-01 Providence decent audience recording, great setlist, Larry's birthday obviously.
Anyway, sorry that is so long and I hope that helps. After all, according to Ulysess U2 fans arent generous and dont help out, do they. This thread is a prime example of that!! LOL