Result of 
 grep -h -R "User-Agent" /var/spool/news/gmane/**|cut -d: -f2|cut -d" " -f2|sort|uniq -c|sort -gr
   1307 G2/1.0
    753 Mozilla/5.0
    483 Mutt/1.5.20
    200 KMail/1.13.5
    120 Mutt/1.5.18
    103 Thunderbird
     78 Alpine
     37 Gnus/5.13
     36 Mutt/1.5.17
     28 quilt/0.48-1
     28 KMail/1.13.3
     25 KMail/1.9.9
     20 Mutt/1.4.2.2i
     20 KMail/1.12.2
     17 Opera
     16 Mutt/1.5.19
     14 quilt/0.48-11.2
     14 Mutt/1.4.1i
     13 Mutt/1.5.20-6127-vl-r38670
     13 KMail/1.9.10
     12 Loom/3.14
     12 KMail/1.13.2
     11 quilt/0.47-15.10
     11 mutt-ng/devel-r804
     11 Mutt/1.3.28i
     10 v=1;
     10 StGIT/0.14.3
     10 Received
     10 Mutt/1.5.17+20080114
     10 Jack
      9 nail
      9 Mozilla-Thunderbird
      8 Notmuch/0.3.1-58-g6607fd6
      8 KMail/1.12.4
      7 Sup/git
      7 quilt/0.47-1
      7 Postbox
      7 Gnus/5.110011
      6 Mutt/1.5.16
      5 Wanderlust/2.15.6
      4 Xnews/2006.08.24
      4 Sup/0.11
      4 StGit/0.15
      4 slrn/pre1.0.0-18
      4 Internet
      4 Gnus/5.1008
      3 (X11;
      3 slrn/0.9.9
      3 Pan/0.133
      3 Mutt/1.5.12-2006-07-14
      3 KNode/0.10.4
      3 Gnus/5.11
      2 Web-Based
      2 slrn/pre0.9.9-102
      2 RoundCube
      2 Mutt/1.4.2.1i
      2 Gnus/5.110009
      2 From
      2 40tude_Dialog/2.0.12.1
      1 StGit/0.15-83-g972d5
      1 SquirrelMail/1.4.9a
      1 SquirrelMail/1.4.8-5.el4.centos.8
      1 SquirrelMail/1.4.6
      1 SquirrelMail/1.4.19
      1 SquirrelMail/1.4.13
      1 slrn/0.9.9p1
      1 NaSMail/1.7
      1 Mutt/1.5.13
      1 Mutt/1.4.2.3i
      1 Mutt
      1 KMail/1.9.5
      1 KMail/1.11.4
      1 Heirloom
      1 Dynamic
      1 curl/7.21.0
      1 curl/7.19.7
      1 #1