Bay, no question. Emmerich can indeed at least compose a scene nicely, even if the movie itself is heavy-handed moralizing. Bay is just...well...
...I think this sums it up pretty nicely (thank you Robot Chicken):
But is Bay the worst director ever? No. Is Boll worse than Bay? Yes, but even he's not the worst! Coleman Francis comes to mind for that award.
Or...God help you if you have seen it without the aid of Joel & The Bots...there is the singular motion picture work of fertilizer salesman Harold P. Warren to consider...