Hello!
Which IRC-Client yould you prefer? Which works well?
Well, I would prefer to use konversation as it looks quite slick and is a native KDE4 app so it fits in well with the KDE4 desktop, but sadly it has a few problems now and then, mainly with DCC file transfers and sound notifications.
So I use xchat, it’s a GTK app, so it has a rather ugly and childlike interface, but DCC functions perfectly and the sounds I assign to events work perfectly.
Xchat is what I have been using since forever.
Konversation aka Konvi 
No problems at all with DCC in konvi for kde4