Both Thanos and Darth Vader are two of the most terrifying villains in their universes, but there's one key power difference between them, and it involves lava. While few rival Vader's abilities and inner-darkness in the Star Wars galaxy, he is still very vulnerable to lava, as he's gone out of his way to avoid falling into the fire. However, Thanos has fallen into the heart of a volcano and come out unscathed.
Darth Vader's dislike of lava in the Star Wars universe is understandable for the villain. Before fully transforming into Vader, Anakin Skywalker battled his former master Obi-Wan Kenobi during the Duel on Mustafar. The fight, which occurred on the fiery planet, ended with Anakin getting maimed by Obi-Wan, as he was left to burn in the lava on Mustafar - further disfiguring the former Jedi. After becoming a Sith Lord, Darth Vader still avoids lava, as it's not only dangerous but traumatizing for him, which is a big power difference from Marvel's Thanos, who has had no problem being directly knocked into a volcano.
Two separate comics illustrate the power difference between Thanos and Darth Vader, and it's how both reacted to falling into lava. In Ka-Zar #11 (1997) by Mark Waid, Andy Kubert, Joe Rosas, Digital Chameleon, Jesse Delperdang, and Todd Klein, Thanos is knocked into a volcano by Ka-Zar while in the Savage Land. Instead of being burned by the lava, Thanos emerges without a scratch, albeit, without his armor. While the version of the Mad Titan who survived the blast would later be retconned to be a clone, it still showed how Thanos is invulnerable to lava.
Meanwhile, in Star Wars #75 from Greg Pak, Phil Noto, and VC's Clayton Cowles from Marvel Comics, Darth Vader's battle against Chewbacca shows how he very much fears lava and being totally burned alive like he almost was on Mustafar. So when Chewbacca knocks him back into the lava, Vader makes sure to part the lava with the Force - narrowly avoiding being burned again in the process.
While Thanos and Darth Vader might live by the same dark philosophy, how they react to being thrown in lava shows the biggest power difference between the Marvel and Star Wars villains. Thanos can be completely covered in lava and emerge unscathed, thanks to his cosmic powers. Meanwhile, Vader does everything that he can to avoid being thrown into lava, knowing that if he were submerged in it, it would be a death wish. Darth Vader can hold his own against most opponents, but when it comes to lava, Thanos has one key power advantage over the powerful Sith Lord.
