R’ Moty Berger of Aish; R’ Akiva Tatz; Rav Yisroel Brog (Cleveland); Rav Shalom Kaminetsky (Philadelphia). All of them are in their own right geniuses in approach and content.
There are also many experts on specific topics such as other beliefs and counter-missionaries. Just ask any organization with a Kiruv training program such as Torah Links in Lakewood.
Hatzlacha!