The brain by far. You could say that the universe is more complex by the sheer number of particles and stuff, but the brain is very nuanced. We are inside the universe and can analyze it all we want, but you don't know anything about what you're thinking. You may think you do, but this is only surface level stuff. You don't know why your brain makes the connections it does or why ideas can pop in your head all of a sudden. The mind is an ocean with random debris coming to the surface, and our chances of understanding distant places through this debris is like the difficulty of understanding the brain.
Technically too the body is more complex than the brain, so I guess the body.