G'Kar is the best character. So much development throughout the series...
Marcus if my favourite.
But there's just something about Vir. I mean, little airhead Vir grows up and becomes the Emperor but is still so innocent even then...
Favourite lines: "Well if it isn't, then it's not. But if it is... Well, there you are." -- Sheridan, A Call to Arms
"I spy with my little eye, something that begins with 'B'"
"Boxes."
"Okay, again. I spy with my little eye, something that begins with 'M'"
"More Boxes."
"One more try. I spy with my little eye, something that begins with 'E'"
"Even more boxes."
--Marcus and Franklin on the way to Mars, Season 4
"You are not The One. And you are not The One. And you are not The One."
--Xathras to Sheridan, Sinclair and Delenn on B4, Season 3
"Xathras tell Xathras not to go, but Xathras never listen to Xathras..."
--Xathras to Ivanova, Season 4
"Do not make us engage your ships."
"Why not?"
--Delenn and the EA fleet commander at the end of the Battle for Babylon 5
"What do you want, Vir Cotto?"
"What do I want? What I want is to be there when they cut off your head and stick it on a pike in the garden. Then I'm going to look up into your lifeless eyes and wave. Just like this."
--Vir and Morden sometime during Season 1
"I really hate it when you do that"
"Good"
--Sheridan and Kosh during Sheridan's education, Season 2
God, it's like "Shoot 'Em Up" There was a great line almost every episode. So hard to remember them all, let alone choose just one.
Edit: I forgot one. Morden and Londo near the end of Morden's life:
"Yes, you ships are Very impressive. In the air or in space. But right now, they are on the ground."
"Our ships can sense an enemy approaching from miles away and be in the air in seconds. So what are you going to do? Blow up the island?"
"Well, now that you mention it..."