Embodied said: ” what is the best way of contemplating a Dhamma concept : images, words or both?”
This is probably an issue of expressing oneself (you and me both).
I think contemplation/thinking/analyzing/seeing whether some idea makes sense, etc. all fit in to that category.
By the way, that is same as the “conscious thinking” component of vaci sankhara: “Correct Meaning of Vacī Sankhāra“.
When one grasp an idea or a concept one’s sanna on that will change according to that. Then that sanna will be in effect automatically.
See, “What is Sañña (Perception)?“.