photographic or illustrated

The answer can actually vary based on what you're creating. I use photographic characters in my scenario-based training to support a more real-world experience and learning environment. My exception is when I've included an illustrated video in the course (character continuity) or if it's a "threatening" topic that may make my learners uncomfortable or even triggered.

With still images, photography tends to lend a greater sense of professionalism and competence. It's also a great way to depict something that is very literal or real-world (like physically writing or typing) because illustration can give a feeling of more abstract or less serious. It can also lend a greater sense of in-person communication as your learner is "meeting eyes" with your character, which can actually build a coaching or shared experience connection. 

In contrast, if you have illustrated video (such as Vyond or PowToon) either in the course or for supplemental learning, using those same illustrated characters gives greater continuity to your story. Illustrated characters can also help make a serious or intimidating topic more approachable and "safe" (sexual harassment, aggressive work environment, extreme safety concerns, workplace intruders...).