Sub Bass should not be directional. It should sound like it's everywhere. I have a Rel B3 which is front firing with a downward port. That said I personally find if I place the front of the sub firing to the left (it's on the right of my right speaker) it sounds like it's coming out of both the right and left channels and is pretty even throughout my room. If I face it right at me either in that position or between the speakers the sub bass seems less except if I walk around the room. Yep I have a pretty bad room... So I would think down-firing would easier to setup and place. I also only add to what my main speakers can't reproduce and NOT ADD to it (then it tends to get directional meaning I know where the sub is).
