I'd go with Agent as my favorite mod, seeing as how his newfound power hasn't gone to his head...he still acts exactly the same, save for his affinity for changing people's names. Plus, I always thought he was a cool guy, so that's a plus.
My least favorite would have to be nikjohns. This guy is the definition of a nazi, not Tom. Tom at least posts his opinions before closing a thread, nik just talks down to everyone, then locks the thread, then another thread, then he dislikes the amount of characters in another thread's title, so he locks that as well.
...Kotz for mod.