I would doubt that anyone except presenters on the conference circuit could attend a sufficiently large cross-section to make a worthwhile judgment, however subjective. Even then, someone who is prominent at a lot of Java or .NET conferences is unlikely to have equal stature in the opposite camp. All this is in addition to the metric for "best".
I like James McGovern, but I find it hard to believe that OWASP Hartford would be high on anybody's best conference list. I'm surprised to see it cited.
I should have noted that the quality of an experience like a conference or a class has several components, of which the presenter is only one. I get the most out of a class or presentation when the material and my ability to absorb it match. A great presentation that's over my head, lacking sufficient context to absorb it, does me little good. Even the best rudimentary material will quickly descend to the level of a retold favorite bedtime story if I'm too too familiar with it. The message and my receptivity have to match.