Aw man.. As with every "what is your favorite CoX [insert topic]", it's pretty much impossible to decide, since CoX has just too many cool zones to pick. After some thinking, here are my favorites :
- Blueside : Faultline. Great story, great design, and the Blueside zone that feels most "alive" (runner up would be Brickstown or Kings Row). It has fantastic architecture and layout, the Arachnos-infested tunnels and the Dam are just awesome. And as mentioned before, the over-arching story makes this zone a must-play on basically every character (especially for Agent G's storyline and the final battle royale between the Arachnos and Sky Raiders lieutenants).
Runner-up : Croatoa (magic town, great story, 'nuff said)
- Hazard Zones : Striga Isle. How many villain groups can actually claim to have their own zone/volcano island? While I may find the Council to be pretty dull (especially compared to the more colorful and punchable 5th Column), Striga stands as one of the most unique and fun blueside zones. From the linear storylines to the amazing TFs, Striga reminds me of Syndrome's island in The Incredibles : full of green and baddies.
Runner-up : Dark Astoria (both the eerie original and Lovecraftian versions are some of the most atmospheric and freaky zones in the game)
- Redside : St. Martial. The Las Vegas of the Rogue Isles, and as others pointed out before me, the one Redside zone which truly feels like what a criminal town would actually look lik. St. Martial makes the player feel like part of a colorful world, and while the playing cards theme certainly helps, the zone's SAs are what makes it truly shine.
Runner-up : Grandville (the Arachnos metropolis, just for how iconic and representative of Recluse's mindset it is)
- Goldside : Imperial City. Probably the most beautiful and realistic city-like zone in the entire game, IMHO. IC makes me feel like a Marvel superhero every time I run the contacts there, just because it looks so much like NYC would look like in a comic book world. Nighttime IC.. is just downright gorgeous.
Runner-up : First Ward (amazing zone design, and who doesn't love a sunken/post-apocalyptic city?)
Here are my two cents about it, at least!