In their regular forms, Thor's strength is primarily due to his Asgardian physiology and the enchanted hammer, Mjolnir. With Mjolnir, Thor's strength is enhanced to god-like levels, enabling him to lift entire planets and engage in cosmic-level battles.
However, when it comes to the specific question of who would win in a fight between the two, the outcome can vary depending on the context, plotline, and narrative choices of the writers and creators involved. In some stories, the Hulk's raw might proves too much even for Thor, while in others, Thor's godly powers, such as his control over lightning and his mystical abilities, give him an edge.
In major crossover events and battles, such as the Ragnarok storyline, both Hulk and Thor have fought alongside each other as allies, demonstrating that their combined might is often more effective against greater cosmic threats than their individual strengths.
Overall, while it's possible to argue the merits of their abilities and strength feats, determining a definitive winner in a Hulk vs. Thor battle is a matter of interpretation and storytelling within the Marvel universe, and the outcome can vary based on the specific circumstances presented in each comic book or storyline.