Ive always saw Lugia as the coolest of the two, but the poster for the twelth movie convinces me otherwise..
Ho-oh's pose looks pretty damn awsome here and makes it look really graceful against the sunset skyline. All I see when I look at lugia however is some sort of deformed dinosaur with overgrown hands and short cubby legs. What I also like about Ho-oh is that its based of a Phoenix, rises from the ashes and literally craps out rainbows. Thats awsome.
Its had little to no screentime compared to other lengendaries, which I like, because its not a ''Look at me, im so awsome!'' sort of pokemon, either. So yeah, im going with Ho-Oh for this one.