In my memory, ICQ had a terrible client. But the protocol could be used with better, less bloated clients (like trillian). And it had features at the time, like offline messages, that came surprisingly late or were missing in other, later clients.
By the same standards, I would of course say Skype has a terrible client now.
ICQ went down the same path most clients seem to go, ie. it got very bloated. At first it was very bare-bones, with some really pleasant file transfer capabilities.
Skype really is history repeating itself. The client is becoming less usable by the day, and for some reason I was selected for a beta test that introduced the "new" flat style, at a huge cost to layout efficiency. It's truly terrible.
By the same standards, I would of course say Skype has a terrible client now.