What’s the best format: chronological or skills/functional?

There are no set criteria of Resume making. Different people go different ways. In my opinion the best way is to go as per your requirement and the goal you want to achieve.
 
If you are a Fresher or a young Executive then you can start with your Objective, follow it up with your educational qualifications, latest being on top and then mention your current professional experience if any, Internship or Project experience follows next and finally any additional qualification, achievements, personal details to round it up. 
 
A Professional with more than 5+ years of experience need to start with their Objective or Introduction. Then they should have a comprehensive Profile Summary which should be focusing on their skills and expertise showcased in a crisp manner. It is imperative to have Core Competencies as they also double up as ‘keywords’ while demonstrating the area of specialization in their career. Follow it up with your Career Accomplishments and then your Corporate Exposure. It is required to mention your acquired skills, training’s or additional qualifications and finally sum it up with your personal details.