In small bowl, mix flours, xanthan gum, baking powder, baking soda and salt with whisk; set aside. In medium bowl, beat eggs, oil, milk, bananas, brown sugar and vanilla with electric mixer on medium speed until well blended. Gradually add flour mixture, beating until well blended. Stir in chocolate chips. Divide batter evenly among muffin cups, filling each about three-fourths full.