The Ambassadors are my Favorite characters (Londo/G'Kar/Delenn)
I don't really have favorites beyond that, I love almost all the B5 Regular and Recurring Characters/Actors.
I never really took to Talia, nearly as much as I took to Lyta in the Pilot (and of course her return), so between the two Pat's Lyta wins out (This is of Course assuming Bester is in a Class All His Own)
Quote, I really Like Delenn's "Only One Human Captain Survived...He is Behind me, You are in front of Me, if you value your Lives...BE SOMEWHERE ELSE" and Of Course "You came much further to say even less" is of course, incredible. So many awesome quotes to choose from.
As Far as everything else, it almost all matters, and adds to the tapestry, so aside, from removing a couple A or B stories and blending S4 ending and Season 5 beginning better I really wouldn't change anything, and can't really pick favorites, because without the building up, you can't have the Wham episodes, so how do you choose if the Building blocks or the Wham is Favorite?