Oh, definitely Season 3, if only for the episode called "100,000 Airplanes". That is one of my favorites.

I also love this speech from Season 4's "20 Hours in America Part II":

"Yet the true measure of a people's strength is how they rise to master that moment when it does arrive. Forty-four people were killed a couple of hours ago at Kennison State University." Shot of Sam and Bruno in tuxes standing near the back, listening. Then a shot of C.J. in a gorgeous white gown, standing near Charlie, both looking sad. "Three swimmers from the men's team were killed and two others are in critical condition, when, after having heard the explosion from their practice facility, they ran into the fire to help get people out. Ran into the fire. The streets of heaven are too crowded with angels tonight. They're our students and our teachers and our parents and our friends. The streets of heaven are too crowded with angels but every time we think we've measured our capacity to meet a challenge we look up and we're reminded that that capacity may well be limitless. This is a time for American heroes. We will do what is hard. We will achieve what is great. This is a time for American heroes and we reach for the stars. God bless their memory, God bless you and God bless the United States of America." Standing ovation. Bruno asks Sam, "When did you write that last part?" Sam: "In the car." Bruno hesitates for a moment and says, "Freak."