That Essentials topic is the one you're looking for. I posted two lists of the "absolute must have" bootlegs. http://www.u2start.com/topic/message/1076/ and the other one is just a few posts below...
Can anyone argue with this list? I tried to compile 2-4 bootlegs from each tour for a friend that's getting into U2 live, and trying to choose shows that were high quality in terms of sound, so he isn't put off by average sound quality:
1980-10-14 Hilversum
1981-05-11 Denver
1981-11-04 Berlin
1981-12-13 Lido Beach
1982-02-11 New Orleans
1982-12-06 London
1983-05-30 Devore
1983-07-02 Torhout
1984-11-21 Dortmund
1985-02-05 Bologna
1985-04-15 East Rutherford
1986-06-15 East Rutherford
1987-04-29 Chicago
1987-07-04 Paris
1987-11-07 Denver
1989-12-01 Osaka
1989-12-30 Dublin
1990-01-10 Rotterdam
1992-05-22 Milan
1992-06-11 Stockholm
1992-09-13 Madison
1993-08-28 Dublin
1997-06-18 Oakland
1997-08-28 Leeds
1997-11-14 Miami
2001-06-22 East Rutherford
2001-08-08 Barcelona
2001-10-27 New York
2005-04-15 Glendale
2005-12-19 Portland
2006-12-09 Honolulu
2009-07-07 Milan
2010-09-26 San Sebastian
2011-06-18 Anaheim
2015-07-06 Toronto
2015-09-13 Amsterdam
Here are some of my favorite shows sound quality on all these I give 5 stars !
2-26-1980 Dublin
3-6-1981 Boston
12-6-1982 London
5-6-1983 Boston
11-21-1984 Dortmund
3-27-1985 Montreal
11-7-1987 Denver
12-27-1989 Dublin
8-28-1993 Dublin
6-18-1997 Oakland IEM
12-2-2001 Miami IEM
11-4-2005 Las Vegas IEM
9-26-2010 San Sebastián IEM
5-14-2011 Mexico City IEM
7-6--2015 Toronto IEM Mix
The intro to Rejoice at that show.... The band intros and then... 'And this is Rejoice!' And the opening guitar... Gorgeous.
As for great bootlegs, I'd highly recommend the Jacksonville TUF show. Very good sound, very strong performances all around. (Can't recall the date, something like 30 April 85?)
Based in mix of great sound quality and performances
1987-07-08 Brussels
1992-04-07 Austin
1992-09-02 Philadelphia
1997-11-23 San Antonio
2001-11-09 Salt Lake City
2005-09-21 Chicago
2009-08-20 Sheffield
2011-07-30 Moncton (heartland source)