assertive,
self-asserting,
self-assertive aggressively self-assured; "an energetic assertive boy who was always ready to argue"; "pointing directly at a listener is an assertive act"
forceful characterized by or full of force or strength (often but not necessarily physical); "a forceful speaker"; "a forceful personality"; "forceful measures"; "a forceful plan for peace"
emphatic -
spoken with emphasis; "an emphatic word"