what is the best enviroment in catia,for designing a car body?
ICEM Shape Design
Generative Shape Design
I don't know about ICEM Shape Design, but mostly I use freestyle and GSD to some extent.
If you just want to start a first styling process, Catia Shape sculpture ist a nice tool.
For serious and parametrc car body design, GSD ist the first and best choice.
I use GSD in my job. I work in the BIW department of an OEM.