Molding Crown Supplies

The Hallway Is Fairly Long, Has A Low Ceiling, And Does Have Naturally Lighting. Now I Am Having A Hard Time Choosing The Best Crown Molding. Should It Be Plain Or Decorative? Should It Be Crown Or Cove? I Want The Hallway To Feel Wider Than It Is And For The Ceiling To Seem As Though It Were High, Or Higher Anyways. And Of Course The Last Thing I Want Is The Opposite, For It To Seem Smaller. Also Suggustions On Size Would Be Great. Thanks!