The best characters to use for your headshot session can easily be chosen by thinking about the type of person you are. If you don't know what kind of person you are, then unfortunately, I don't think I'll be able to help you. Remember: you should always go for roles you play well if you want to be successful. Therefore, you should also make sure those roles show up in your headshots. Remember that the easier it is for you to play a role, the better you'll play it and the more jobs you'll get. This is called branding, or typecasting yourself into a specific style or character.
It's always good to learn new techniques and be able to play different roles, but you definitely should make an effort to become known as a certain type of character. And to do that, you need to establish that character in all of your headshots so that the casting directors know who you are.
Choose a specific role, then think of some of the best expressions to show that role off. Practice them and then use them!
Hey I'm Martin, and my goal is to help you reach yours. I love writing content about career advancement, marketing strategies, productivity, and much more.