Best: Skingrad, because I love the architecture there, and the NPCs are all pretty cool. Bruma is a close second, though.
Worst: Anvil, seems too crowded and the NPCs bore me to death for some reason.
Nice thread, by the way. I'd never expect someone to ask about people's opinions on their liking of FG halls. (But I am glad you did, gave me something to think about for a moment.)