Thor 3 is basically a full blown comedy. It's takes the leap from "some comic relief" to just full blown comedy and jokes every 15 seconds.
Black Panther wins this fairly easily.
They actually kinda have a similar plot ... both deal with a main hero who has the burden of taking over as king after the death of their father. And even the villains are kind of similar. But Black Panther basically handles that set up 10x better and doesn't undercut itself by not taking things seriously. It's fun and has humor but doesn't totally kill the tension.