Quasar. In his own series he was starting to get there at times, but just not often enough. And in his most recent appearances the writers are unfortunately back to portraying him as lacking confidence and awed by other herald types like he was years ago.
He has a very wide range of powers - generation, manipulation, and absorption across the entire electromagnetic spectrum, some level of direct manipulation of gravity, shields and constructs, interstellar range teleportation, access to a dimension of limitless power. And his power comes from extremely powerful cosmic artifacts.
He is also supposed to be quite intelligent, with some training in physics and as a SHIELD agent, which more could be made of.
There have been hints over the years that the bands are even more powerful than he knows, with other powers yet to be found - maybe psi powers, maybe strength amping, maybe even immortality, plus glimpses of control over other energies outside e/m. We've seen that he can do heat and magnetic control, light manipulation like holograms and invisibility, but he rarely does or never does again. He doesn't make much use of electricity.
I just think there are a ton of ways he could use his powers outside what he does and a lot of potential power left to discover.