Alex Ross works both for Marvel and DC, and here is his answer when he asked to choose between the two.
Alex Ross, and gave a unique look for each characters, More humanly natural, More realistic suits, No exaggerating muscles popping-out of their spandex.
Avengers by Alex Ross
Justice League by Alex Ross
But in a Interview for up coming book named MARVELOCITY, he answered the question many fans have been arguing about, "Marvel or DC", and this is his answer:
Here is what he tells about Marvel Comics:
“What’s always separated the two for me is Marvel’s material has always had a kinetic quality to it, particularly based on the design aesthetics of Steve Ditko and Jack Kirby,”
“DC characters are not defined by a singular artistic voice influencing all the rest, but that’s what happened with Jack Kirby’s leadership of the entire Marvel brand. Everything is affected by what he led the charge of. That 10 years where he created the majority of those characters in the ’60s, that’s what every artist and writer has built their process upon, including the movies today.”
Here is what he tells about DC Comics:
"DC is the foremost component of where the DNA of what makes a superhero came from. They did the very first superhero in Superman, and the first great embodiment of the dark superhero in Batman, and of course the first female superhero in Wonder Woman."
The Marvel characters are all over the place in terms of what makes them unique, and there’s a hip energy that’s been instilled in them since their creation. Every other superhero company follows the mold of having their heroes follow those archetypes that DC embodies, but Marvel broke away."
Source: COMICBOOKMOVIE