I like David Wood, he and his friend Sam Shamoun, are both Christian Apologists to muslims.
Robert Spencer has studied islam more then both of them. But my favorite teacher of islam is
Christian_ Prince. He, as an islamic scholar has studied all the hadiths. Arabic is his first language.
My in depth knowledge of islam has come from these Apologists. I also like Pamela Geller,
she and Robert Spencer have contributed a lot to waking up the world to the threat of islam.