re: Marvel vs DC - Who has the better cosmic setting?

Marvel's cosmic setting is the most in-depth and best developed of the two. From the Celestials to Galactus to The Stranger to Eternity to The Beyonder/Rubik to the Eternals to the Skrulls to the Kree to the Brood to the Badoon, to... etc.

While the DC Universe has some cosmic-ness, it's limited and some of it (like Phantom Stranger) delves into mysticism more than cosmic. Hell, there are even in-depth flow charts of the Marvel hierarchy.

LINK

Not only is the Marvel cosmic crowd larger and better delineated, there is more interaction with it among the common titles. Spiderman has held the Uni-power, the Silver Surfer has fought alongside and against everyone, The Watcher constantly breaks his word and do I even need to mention the Secret Wars/Beyonder? Kree/Skrull War?

DC's cosmic-level characters are more sparsely used as their stories (aside from GL) center far more on Earth and other humans.

tl;dr - Marvel's cosmic aspect is larger and has always seemed better-used, better-organized and better-managed to me.