I voted for Luthor, but the two are scary in different ways.
Luthor is out for pleasure and power for himself, plain and simple. Trask actually has a very good motive -- trying to defend the earth from alien invasions. The New Krypton arc proved him correct in being concerned about such an invasion; indeed, a story could easily be written (and probably has been, although I don't know of such a one) which could make the case that if it weren't for Trask's foresight, the Kryptonite gas which ultimately defeated Nor might never have been made in time, and humanity might have perished.
Trask is a villain not because of his motive but because of the means he chose to achieve it. He was paranoid and delusional and firmly believed that the ends justified the means. (Of course, Lois -- with all of her breaking and entering -- also seems to subscribe to a similar view regarding means and ends, just on a smaller scale and with more limits.)
Also, what you see with Trask is what you get. He is not into deception*. In contrast, Luthor revels in mind games and delights in appearing to be a good guy to the world at large.
Their motives and modi opernadi are so different that the choice of which to use in a story would be fairly easy for me once I knew what I needed the villain to do. If, hypothetically, I were writing a story in which the proper motivation for villainy could be ascribed equally to Luthor or Trask, and if I wanted more of a psychological thriller, I'd use Luthor. If I wanted the threat to be immediate and at the hands of the villain himself, I'd go with Trask. If subordinates were involved to do the dirty work, I would look at the rest of the story and see if either character would 'fit' better.
I can't really give a simple answer to this question. Maybe I should have voted for 'other'.
Joy,
Lynn
* edit: Well, except for the phony warrant; but the fact that the good guys realized so quickly that it was phony shows to me that he doesn't do deception particularly well.
