I think I have to go with the First Contact scene. Picard goes through rage, then an eerie calm, then his Ahab speech. You think he's calmed down then he talks about how the Borg have attacked Federation ships, assimilated entire populations and fall back. He's gradually building to his 'this far and no farther' speech. His Generations speech was moving as well, but the cycle of emotions in First Contact beat it out. As someone else noted his reaction on the holodeck when he first read the report was effective as well. His speech in Insurrection to Admiral Dougherty was good, but it was normal Patrick Stewart fair. He is always good at making those sorts of speeches. In Nemesis the same thing. The diplomat in Picard effectively acted by Stewart. I did like his speech to Schinzon on Romulus when he told him nothing would make him prouder than to take his hand in friendship. That is after all one of the highest ideal of the Federation, peace for all.