I like the guards comments when you are wearing Ebony Armor and Steel Armor.
"By Ysmir! Is that... ebony? What I wouldn't give to have a set of that!"
There are certainly at least two triggers for the comments. Faction status and equipped items, but which takes precedence seems a mystery. They may be specific like the ebony comment, or the one you get by carrying the shield Peryite gives you. But most of the gear comments by the guards are odd, though. Like, "the gods gave you two hands for your weapon, and you use them both. I can appreciate that," even when I'm most emphatically carrying a 1h sword and board. Maybe she meant my bow? "Light armor means light on your feet. Smart," is usually closer to the mark.
The other things are more specific. Since this guy is almost entirely in DB gear, I hear, "psst! Hey, I know you. Hail Sithis!" which makes sense, but though I don't have a stitch of TG gear (but am the head honcho there) I often get, "hands to yourself, sneak-thief!" or, "if I find your hand in my pocket, I'm going to cut it off!" This latter one is puzzling. Cut off what? My hand? His pocket?

Similar to the TG thing are the CoW comments. This guy is not a mage at all, but often hears stuff like, "so you can cast a few spells. Am I supposed to be impressed?" or "why don't you conjure me up a warm bed" or "why are you messing around with Saarthal?" or however that goes.
Farengar doesn't have much variety in his dialog, but next time approach him with the Candlelight spell active.