I also loved Babel from season 1, but it isn't a favorite. If I had to pick one, it would by Way of the Warrior. There are lots of awesome quotes, space battles, and character moments. I've probably got the whole thing memorized, in fact in the line by line thread, I always know the line that comes next. Sad I know, but when I was 15, I got this episode as part of the Greatest Battles VHS set with TOS Battle of Terror, TNG Gambit, and VGR Maneuvers. The only one that got watched enough to be quoted was WotW.