General:
* City
* Metropolitan
* Civic
* Municipal
* Town
* Built-up
* Conurbation (a continuous urban area formed by the merging of multiple towns or cities)
More specific:
* Modern (for a modern city)
* Industrial (for a city with a strong industrial base)
* Cosmopolitan (for a diverse and international city)
* Crowded (for a densely populated city)
* Fast-paced (for a city with a quick and busy lifestyle)
Opposites:
* Rural
* Country
* Suburban (which is technically between urban and rural)
* Provincial
* Outlying
The best synonym to use will depend on the specific meaning you are trying to convey.