What is the difference between carbon and cocoa ? For what type of applications we should use carbon and for what type of applications we should use cocoa ? Which is the best of both for developing applications in Mac OS ?
Carbon was created to ease the movement to and from Mac OS 8 and 9. If your code needs to run under OS 8 or 9, then Carbon is the way to go. (Source)
However, if your software is designed for OS X, then you should emphasize Cocoa over Carbon.