Will I have more success as a Full Stack or front/back end developer?

I am a mid level full Stack Developer. I enjoy working on all areas of the Stack, but I have started to try to move towards the more senior rank and I am wondering if being a specialist in one particular area will make me more employable/valuable. An alternative I'm thinking of is just to spend time working on my JavaScript(react, node) skill set and presenting myself as a JavaScript full Stack Developer. I'd love to hear everyone's opinions and experiences.