Found this online which will not ruin anything about the characters but briefly describes the differences between their approaches.
And both characters are right for their stories. There are many different types of villains; some want to destroy the world simply because they are bad, others have motivations that we can understand and even agree with. And it depends on the story as to which one it needs. A story like Lord of the Rings needs a villain who is just unstoppable evil, whereas a movie like Avengers: Infinity War requires someone like Thanos who makes sense, despite how vile his methods are.
Likewise, for Harry’s story, Voldemort was the required villain, because Harry needed to face someone who was undeniably evil. When Voldemort walked into a scene, we all held our breath. But with the Fantastic Beasts series, a more nuanced villain is called for. This is a more grown-up story we are experiencing now, and it calls for more gray areas. It calls for an antagonist who can be reasonable, and has the ability to sway even the best characters. We know- because of the books- that Grindelwald will go down as one of the darkest wizards of the age, and that he will be stopped. But now we get to see why he was regarded in that way, we get to see how he was dangerous, and learn how different he was from Voldemort.