Windows: WSAASyncSelect VS IOCP Completion Port and overlapped IO

Not one time i hear from people recomendation using boost::asio instead QtNetwork. I compare source and descriptions both library for Windows implementation. And Qt and asio using Overlapped I/O, but Qt use WSAASyncSelect for receive sockets events, asio use IOCP (Completion Port). How about migrate to IOCP too? People say what IOCP get more stability for server and this also get reason for remove CreateWindow from QEventDispatcher_win.cpp