well... it's both, in my experience.
thoughts control me when I allow thoughts to take control.
when I am present, aware of my thoughts, and observing their impact on me.... then I am able to choose whether to allow my thoughts to own my response and my body and my emotions.....
when I am present and aware of my thoughts, I am able to choose other thoughts. I am able to respond to my thoughts. I am able to choose to let go of thoughts..... I am in a position, then, to choose how thoughts will or will not impact me.
it's only when I'm on 'auto pilot' and letting the thoughts lead onward to other thoughts in a spiraling chain of thinking that those thoughts begin to control me.