I´ve been an exchange student and our family hosted two exchange students aswell. We went with AFS, because it´s non-profit (like YFU) and prepares both students and host-familys very carefully.
Hosting an exchange student can enrichen your life so much, it can open a whole new world both for your family (and kids!) and the student.
If you´d like more information on AFS:
www.afs.org