Kochi or Cohin is a wonderful coastal city to live in. Kochi comes under Ernakulam district of Kerala and According to Wikipedia, Kochi is considered as the financial, commercial and industrial capital of Kerala.
Marine drive area is considered as one of the most favorite area for upscale living in Kerala, but this area is probably the most costly one too.
The second best can easily be M. G. Road area which is well connected and offers easy access to all the amenities one may need for comfortable living.
Ravipuram area is a little outside, so if you are after a peaceful area a little outer than the main city, then Ravipuram area will suit you. Among other areas that are widely liked for residential purpose are Edappally, Tripunithura, Pachalam, Mamangalam, Ponekkara and Elamakkara.