I personally don't like QQ. It provides a lot of functionality, yes, but overall it is awful and ugly.
The mobile version is better, though. Weixin on the other hand is pure gold, really like that one.
(If you don't mind the fact that both services are provided by a Chinese company

).
I think Psychophanta should try to give Skype another go, it might have improved (not that it is any better security wise).
I don't know any non-Asians that are actually using QQ and not that many use Weixin, so that might be a factor here to be considered.