Cianwood City and Ecruteak City both come up level...
Cianwood
- Nice, relaxing theme, which never seems to get going...which I like.
- You can capture wild Shuckle there.
- Near to Routes 47/8, which have brilliant themes, also providing access to Safari Zone and EmbeddedTower.
- Close to the Whirl Islands, where I can get Horsea and Mantine!
- It's sandy, which makes it unique.
- Chuck has a Poliwrath, which makes him epic win.
Ecruteak City
- Again, nice theme.
- The design of the buildings is nice.
- Burned Tower! I like the music, and have fond memories of entering with a lv.16 Togepi, and leaving with a lv.35 Togetic whilst looking for a Magmar.
- Bell Tower! Good music, and it just has a slightly more "epic" feel to it when you ascend the tower to capture Ho-oh...I just wish more people in Ecruteak acknowledged it.
- Bellchime Trail! It's incredibly pretty, and the first PokeGear registry for a gym leader was made there.
- Thanks to trees (I like to headbutt the orange ones) and water, there is large pokemon diversity in the city itself.
- It's close to Route 38/9, and Mount Mortar, both of which I like.
Overall...I'm saying Cianwood City, just to be different ;)