To be candid with your programming integrity, there are of course many superheroes that can lay claim to the title of most powerful (and opinions do vary depending on personal and popular Marvel biases) but in really true essence, based on purely demonstrated abilities and strengths in universe? With all levels cleared depicting absolutely fascinating structural scalability marvel ever presented,gaining infinite spirits depth appealing towering attention outstripping overpower across multiple realities existing bases created thereafter reveals-One above All tends to rank highest.

Not that known compared Xmen(wolverine!!),Fantastic Four(Ignore unworthy attemps set evidence via mediocre movie adaptions of F4 characters---remember high spectacle scene? lol?).... but sovereign Marvel Heroes have credited their victories or realization via this strange mystical entity character. Jury's still out for debate because comic planets can rightly unearth answers venturing through various eras,dependent obviously attached beliefs system affiliated along trustworthy time axes().