Not on the same level as MM he is about strength level with Superman + have some quiet nice abilities to that would make Sentry wish he had never been born.
Sentry is at least comparable to Superman with strength, also he has super speed (most likely lightspeed), can project hard light constructs and various typical superman abilities, minus heat vision, super breath. Anyway ability wise Jonn has him beat but since people generally agree that Superman can be Jonn, and Jonn has to amp himself to compete with Supes physically, I think Sentry takes it. Also stalemating Genis and Collective are things I don't think Jonn could do. I personally consider Genis over the top GL's/Sentinel (Kyle, Hal, Alan) and I don't think Jonn could hang with them for long. Vote Sentry.
This is really a close one, an heraldbreaking Sentry vs the incredible Hul.... Martian Manhunter. Anyway, MM takes 7-8/10, he is longer in the buisness, the expierience wins this, powerwise they are almost equals.
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Sentry might be comparable to Supes, but neither him nor supes are that good of a fighter. Jon Jonnz isn't that much of a fighter either. However, Sentry should be able to overcome the Martian Manhunters shape-changing abilties and win.
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Damn this is a close one i'ma gonna go with Martain Manhunter for now the man just has more feats and earned his props where Sentry still is relativly new and have to earn his ....
So john john'z 8/10
The only advantage besides possibly intelligence that Jonn has over Sentry is his ability to become intangible, besides that I don't see him winning. Sentry is faster, stronger, a cold/calculting killer and probably more durable. The only way I can see Jonn winning this is if he goes both invisible and intangible and phases inside of Sentry's brain.
Sentry is quite vulnerable to psychic attacks. He has an extremely fragile mind. MM simply mindrapes him and confuses Sentry with his multi-personality disorder.
Allowing J'onn enough time to phase a rock in his skull....
If Jonn even goes into his mind, hes in some trouble. The Void has on occassion incapacitated people who've entered Sentry's mind, however thats not to say Jonn isn't a top tier psychic, I'm just saying there are safer ways to secure a win. In the end if Jonn mentaly attacks Sentry it'll be him (IMO) who'll be left open to attack.
I don't believe Sentry is really weak against telepathy at all. His powers were described as being held together by a strong mental force. Mastermind even said his powers work best on people with strong minds for some unknown reason and he mentally dominated Sentry with no problem.
J'onn has withstood the mind of the Joker, the Spectre, the Overmind of the Presence, Mageddon, Neron, Darkseid, Parallax, and even the Source.
A man with a multiple personality disorder isn't going to phase him...
J'onn can multi-task. Which is what he does quite often. He can connect with every being on Earth, probe their minds, run algorithims with Oracle and fight Ultraman to a bloody pulp. J'onn simply shapeshifts his own brain to several lobes dedicated to several tasks.
And he really only has two. Mindrape Sentry and physically beat him down. Or simply turn intangible and let Sentry swipe thin air as MM invades his mind and fractures his already f'ed up psyche.