Both should shut their mouths and stop singing. Oh wait, they can't sing. They try to trick people into thinking they can by glossing up their voices with studio magic. Have you ever heard them sing live? Not lipsynching, but LIVE. Nope, I haven't. My cousin has Hilary Duff's concert DVD and she lipsynched through the whole thing. I didn't hear a song that sounded different from the album.
Btw, when they both 'sing', they sound alike. When I first heard Lindsay's "Rumors", I thought it was Hilary Duff.