Woot the thread has been made!
I say Michael could defeat Lucifer, Michaels will is equal to Lucifer's will depending on how you percieve the story from the begining to the end, this means their powers are about equal but in different perspectives.
Michael has defeated Lucifer in combat in the war of the begining, the blast that Lucifer survived when he impaled Michael out side of existence was very weak in terms of sheer power; the evidence that supports that is that first Michael was very weak from years of torture, secondly Michael when focusing does not have universal power but uncalculable power since he is the power of DC's god.
Michael later in the series (story) becomes "one" with the logoz, Michael and Lucifer both have great power, and they both have equally great wills, Lucifers strength was that he always had a desire to fulfill no matter, Michael's will was to please god or depending on how you look at it to be with god and go on with him no matter what, and in the end they both fulfilled their wills.
Lucifer chose not to lose his desire, his passion, he chose not to become one with god.
Michael chose to continue through all, to lose all, he chose to become one with god, depending on how you look at it, to go on with god.
P.S. It wasn't that Michael could not kill Lucifer, it was that he was not meant too, remember that yaweh told Lucifer that everything has purpose and that despises waste. Every single thing that happened, from lucifer rebelling and leading others, to Michael riding out against lucifer, that everything has purpose and meaning to his plan.
P.S.S. Michael and Lucifer are like different aspects of DC's god incarnated, each with the polar opposite of the other yet both having half and each being all of DC's god.