Question: How complex should a character's personality be? I don't want my characters to be extremely simple, but I'm not sure if a complicated personality would be too hard to grasp.Answer:
It depends somewhat on what type of story you are writing. Some stories are more plot/action based. They may have simpler characters because complex exploration of personalities would slow the action too much. Archetypal characters often work well in such stories.
On the other hand, some stories are more character/decision based. They may have simpler plots because the focus is more on in-depth character deliberations.
You have to know what genre you're writing in and perhaps what the readers expect to know what is appropriate. Or sometimes you just write the kind of story that would appeal to you and maybe you create an interesting twist on an existing genre.
Incidentally, even in a plot/action story, you still want well-rounded characters, you just have to paint them with fewer, broader brushstrokes.