I guess in rethinking it, Buffy spends more time in the IC (visiting the shops and the University) than any other city. That is because she travels so much that it seems she is always passing by the IC enroute to somewhere. Yeah, I bet she spends more time there than even her home town of Bravil.

Most visited:

Leyawiin. I really like the layout of the city and it also contains my favorite house, is near my favorite cave (Rockmilk) and fort (Fort Doublcross).

Skingrad. I like that this city is sort of in the center of the map. It's a nice halfway point to wherever you want to go.

Least visited:

Bravil: I can't really explain this one. I just don't like the way it looks.

At the moment, Bruma, because it's the closest I can get to Skyrim