What are the main differences between Marvel and DC comics?

Obviously any one writer can be put in either companies universe and tell a good story. I'm sure both Companies have serious and Campy characters under their belts.

I dont read comics and only know characters from both universes from the various cartoons/movies. Is there no actual difference? Are the Avengers the same as the Justice league and perform the same role? Or is there a tangible difference between the tone/atmosphere of the general universes. This isn't about who's "better", I dont care.

Teach me nerds.