Illustrator is the industry standard, with good reason, for creating illustrations, typography-focused design, and just simply amazing images for any purpose. It's power partially lies in it's vector focus - you can make a piece that is 1 inch tall, and yet it can be output to a 14' billboard, and it still looks great!
For elearning, the power here is that complex shapes can be made in Illustrator, but then they can be converted through Powerpoint, which just about everybody has, and those vectors are editable in Storyline 360. I use this function almost daily, and it works everytime. Of course, you have to verify that everything is paths from start to finish - no photos, but then you are set.
There are a few tricky challenges to work around, such as not using the gradient mesh if you need to edit in Powerpoint or SL, removing bitmap effects such as drop shadows, and being careful with transparency, but altogether this is a great workflow, that just takes some experimenting to get a much more effective and versatile outcome than Powerpoint or Storyline alone.
