In pure telepathic battle, MM might defeat even Nate.
With the Martian race having evolved out of a predominantly nomadic race of creatures, telepathy was their natural means of communication which over the centuries the Martians were able to craft into a highly effective state, coming known to be the most adept psions in the cosmos. Now, being the last of his kind, J'onn's mind is often regarded as being the most adept in all of the universe, though technically there are minds greater in power than his (Hector Hammond for example) there is no one that more skilled in the arts of the mind than he. Seen as a premier hero all over the world, beings from all over the cosmos revere the Martian for his psionic abilities and knowledge, making him the foremost authority on the powers of the mind anywhere.Requiring little to no effort to read the thoughts of those around him, only those of shielded minds can hide their thinking from the Martian, as he can reason through even those from an insane man (though those of an advanced state of insanity such as the Joker are far too erratic for him). Skilled in the practice of sorting through memories and associated thoughts related to emotions, he can reason though the minds of most anyone from any background, language, or race as he can even communicate typically with completely unknown entities. As long as a source has a mind, no matter how bizarrely sentient, J'onn can find some means to make at least a basic contact.
Having organized his mind into a Mental Mansion, he has attempted to put a manifested form to his own mind in order to be able to organize his own mind all the better. Essentially now, J'onn's mind is divided in a mansion-like structure, with each identity he has having its own room, one full of memories and thoughts and emotions, that to assume all he needs to do is to open that door and enter the room. At the core of this Mental Mansion is the Library in the Cellar, where all of his own personal memories are stored.
What can block or break down J'onn's telepathy is his ultimate weakness, that of fire. Fire, to a Martian, calls upon their most primal aspects of their minds, eroding away at their thoughts and descending them into a kind of madness that sees them destroying themselves. Unable to escape this allure, in the presence of flames J'onn is only able to focus on other things with great concentration and should he come in contact with a flame, he would become instantly lost to this failing. Causing physical trauma as well, the presence of fire will cause J'onn to cease all of his telepathic abilities.
Not having the most powerful of psionic minds, J'onn does have the most skilled so while his mental assaults may not always be the most overpowering, they are often very skilled and precisely effective. All of his offense uses are very draining to J'onn physically, as to the Martian body and mind are interwoven so intricately that to use his telepathy in an invasive manner traumatizes him to the point of physical exertion. Even the smallest of offense uses drains J'onn to some degree, and the more powerful or intricate the attack, the greater the strain on his body he risks as high end stunts will cause him to collapse into unconsciousness. It is possible for him to exert his mind so much that he could cause his own death.
Not only able to read thoughts, J'onn can also exert his mind over that of others, projecting thoughts and memories into a being to such a degree that they are believable. In effect creating an illusion of what isn't really there; he tricks the mind into believing that it is or even fooling it into not seeing what is plainly there. By extension, he can also edit the memories or thoughts of others, removing or even implanting false ones, and even whole identities. J'onn can also place skills and other blocks of knowledge in the minds of others, that can be known to the mind instantly or even be time delayed to emerge after a specific time or event, in a version of a kind of post-hypnotic suggestion. He can even block select thoughts in others, preventing them from remembering certain things, from memories to even how to use a skill or power.
The height of his telepathic might can be summoned forth for a devastating psionic blast which assaults the target mind with a surge of traumatizing memories and thoughts in efforts to overpower it to unconsciousness. Yet the use f this is typically a last resort for J'onn, as it is nearly as draining for him as it is for his victim.
No one is more skilled in the management of psionic skills than J'onn J'onzz. While there are other telepaths with greater power, J'onn is by and large the foremost expert on the subject. From the development of mental fortitudes to the management of his many personalities and filing of memories, J'onn is the greatest authority on the subject. While J'onn is by no means the most powerful telepath in the world, he is decidedly the most skilled in controlling the power that he has. As a martian, he has discovered avenues for his telepathy that normal telepaths haven't been able to. Also, as a man greatly skilled in espionage, J'onn has learned to use his telepathy in subversive and undetectable (to anyone by superior level telepaths and those who know their mind) methods.
Nobody is better in telepathic skill then J'onn...but some may have more raw power then him.