Hello, I would like to take part in this discussion, hope we have a good time.
Pica would have been easily been angered by All Might due to not liking someone laughing at his high pitched voice, and considering All Might standard way of making an appearance and personality, the former is going to hear a lot of that regardless. Which would make Pica be angered greatly and cause him to go on a rampage. Pica would stay in his giant form and try to squash All Might. I think All Might is far more mobile due to his size and have fast travel speed to move around. The advantage I see is that All Might has superior AP and mobility and Pica has the ability to merge with stone and could move around it.
From the start of the battle where he saved the heroes, he would have seen Pica assimilating the stone and become the stone giant, All Might would most likely deduce that Pica is inside the giant golem, sooner or later or even in that moment he would have tried to the same tactic of Zoro or at least something similar. All Might have fought hundreds of criminal with a variety of Quirks, and there are Quirk that could alter the environment, he even know a hero that could manipulate the landscape of rock(minus the merging, and admittedly, since this is his prime he may or may not met Cementoss before fighting All For One). So it isn't that far off of the assumption that he would know how to deal with an ability similar to Pica. I think All Might had the strength rip the stone golem off the ground and throw it into the air similar to Zoro.
In fact, there is similar Quirk at least in the application, Mimicry(coincidentally, the user is also prone to anger from insults). Although, All Might have not fought said Quirk user, though since there is a character with similar ability should not be discounted.
All Might have the AP advantage. Of course, the question is whether or not he could find Pica's real body before the stone golem could reach the ground, and with the latter Haki, it will prove hard to find Pica since he could move around the giant Golem. Although I think he could pull off since has shown to do 300 punch in a short timeframe and would be able to shave off the stone into small pieces and found Pica. and unlike Zoro, his range is far more wider and longer range and could shear stone and metal even in his weakened state.
All Might has shown to have great reflex and multitask before including in midair crisis where he had punched a tower, collect its rubbles, save a bunch of animals, clear out the area, took a selfie, and put down the dome safely and did a pose, all before CC and Koichi could fall to the ground and also save them after that. Gravity would still remain the same and he had done a lot under those limitations. All Might has shown to have great control in his smash as he had a create a tornado to trap an explosion.
In my opinion I think he could find Pica sooner or later and could punch him out of his stone shell(though this is just a thought and a probability of me being hyperbole as they would say, but what is really stopping All Might from just keeping the Pica stone giant in midair by just juggling it or punching until he searches each and every rock? He has shown to have that much control.)
And so due to having a greater AP, could punch in a quick rate, long range and wide attacks, high reflex, could multitask, have the experience to think of a way to beat Pica and just being a type of guy that would anger Pica a lot, my vote would be All Might.
