XChat is the best client out there, in my oppinion.
Still, i found one thing annoying:
WALLOPs, NOTIFYs and CTCPs should go into the main
network window (or a separate window).
Currently they go into the active window, or if the
network window is the active, they go into the last
channel window :-/
Platform: Debian sid - Linux 2.6.6 [i686]