Juggernaut's upper levels of strength are still unknown according to the good people at Marvel and therefore it is almost impossible to say who is the weakest being that could take him down in a pure slugfest.
Onslaught has done it, but that was pretty lazy writing, with no comprehension of the source of Juggy's power.
Hulk could possibly do it as the upper levels of his strength are also undiscovered.
It is unlikeley that anyone weaker than Hulk could tho.
what could Juggernaugt do against cloak ? this is my argument for the Cloak vs juggernaught argument..... i am going to argue that Cloak could really screw up cain anyday.. he isnt very mentaly ballanced to begin with and could easily get his mind destroyed with a one way trip through the darkforce dimention
Originally posted by wxyz
Assuming Juggernaut at full power, Onslaught, or WBH.
Onslaught didn't beat him in a slugfest. He ripped the gem out of his chest despite it being in space at the time just so that very thing couldn't happen, then punched him across the country after he was weakened.
Now could he win a slugfest? Potentially, since it took a mindless Hulk to break his armor(which was also orchestrated by him), but we never saw him actually slug it out with Cain.