1. Skingrad, Has the largest, best house in the game, so I visited skingrad about once every 30 minuets to store loot.
2. Anvil, Lots of fun quests in anvil, a few fighters guild quests here too, and fort strand is my heavy armour farming location. Also has a blacksmith right next to the gate.
3. Imperial City, visited the market district if I ever had to sell anything of high value, or buy something specific, and done a lot of arena stuff. I cannot even remember visiting the elven gardens district while playing.
4. Bruma, useful while doing the main quest.
5. Leyawiin, useful doing fighters guild quests, and also near Rockmilk cave, my favourite loot farming site.
6. Chorol, Useful doing fighters guild quests
7. Cheydinhal, Useful doing fighters guild quests
8. Bravil, visited it perhaps 4 times in the whole game.