I always saw Marvel Cosmic as the more chaotic one, DC Cosmic was the one that had the intergalactic police force with the Green Lantern Corps whereas the Marvel equivalent, the Novas, were killed off and never came back as far as I know. But one advantage to something like the United Planets is it lets you define Earth’s position in the galactic pecking order. Do the other worlds like/respect Earth? Just how strong are the other worlds in relation to Earth? It also lets you hopefully flesh out some of the worlds besides Thanagar, Krypton, and Raan which are basically the ONLY three worlds that get any focus.
Multiversity was great for mapping out the Multiverse because it led to more consistent usage of the other Earths. I’m hopeful that the United Planets will do that for Earth 0.