I think it was during Clinton's election, when a young Obama stood up and rocked the audience with an optimistic message that had everyone asking "who is that guy?". The Newtown speech was one that had to be made, and about anybody with a heart could have made it. Obama is very good at evoking emotions and making courageous statements, his power is that you know he believes what he is saying.
I suppose you'd have to explain what best means and to whom. His Giffords speech was better in this regards. This speech was flat and disingenuous and made a shameless political move to push gun control. As a person who sees through this phony politician, I don't see it as an even good shout out to his base.
I found his speech to be really engaging, however it pales in comparison to his first inauguration speech. That speech, to a crowd of thousands instilled the hope for change that so many of his constituents believed in.
The Newtown speech on the other hand had a far more somber tone to it and simply didn't inspire people to be better. It was important, but again, it wasn't his best speech as president.
Although President Obama gave an amazing speech for the Newtown tragedy, his speech after he won his second term as President was very inspirational, and it shed attention on the fact that we as a country need to start appreciating people for their differences in order to move forward as a country.