Not to say that writing and acting themselves are similar at all. They aren't. While acting is for the exuberant extrovert, writing is for the quiet introvert.
But, when I'm acting and when I'm writing, some of the same exact feelings surface. To be a good actress, you have to totally immerse yourself in your character. So, for my character, who's kind of off-the-wall, I have to wholeheartedly believe that I invented cheese and banana bread. I have to be over-the-top and extravagant in a way that I'm totally not.
With both writing and acting, you have to work toward something. It'll never be perfect the first time around. The first interpretation will always be wrong. You go through multiple "drafts' and "revisions" each one getting closer and closer to the end product that you'll eventually be proud of.
So whether you like being behind the scenes doing the writing, or on the stage performing the written word, you get the chance to become something you aren't. You get to tell a story. You get a chance to be so deep and involved, and almost become the story.
So writer or actor?
How about storyteller.