My take.
Layton was very good, and just about knocked out Ignatieff with his attendance jab
Harper was steady, uninspiring as a personality as he always is, but clear enough in his message
Ignatieff was all over the place and at times looked downright childish, he failed to show he is ready to become PM
Duceppe is irrelevant, and brought nothing useful to the debates whatsoever.
So honestly I think Ignatieff did the worst, because he had the most to gain, but I doubt his performance is going to make any difference in swaying votes his way.