The best is, place large speakers at ear level (1m above the ground when you're sitting) Subwoofers on the ground of course and if you want to fill the room completely mount small speakers (10" or smaller) high up on the wall. If they are angled down, they are quieter, because the wall itself can add up to some more db if the speaker points to the other corner of the wall (Basically: Front-Right points to rear-right and front-left points to rear-left). In my case, I have four speakers in each corner and a Sub.
If you have a large room (50sq metres or more), the best you can have are Horns, or at least folded horns.