I would be hesitant to use the first two right now. They're heavily used for very visible piracy.
but for corporate file sharing, i would recommend renting a VPS and organizing some simple SSH-based copying with FileZilla, for example. Or some HTTP-based sharing if you want.
Tell that to the pirate bay.
http://www.youtube.com/watch?v=ANTDkfkoBaI
:)
but Sharereactor was designed for exchanging movies illegally, whereas rapidshare tries to be different :)