Personally I've always thought it was harder because some of the bigger DC heroes have been more archetypes so they have harder personalities to pin down on screen when they're all made to be perfect demi-gods
it's been Supermans biggest problem for a long time younger people generally don't like Superman becasue they view him as a boyscout with no weakness. Harder for people to relate to or simply find "cool" as opposed to Marvel characters that people can have fun with.
On the flip-side I do think if done right a Justice league movie could be a lot better than The Avengers.
The director for the Suicide squad has been posting photos from the set. it looks like this version of the joker will be more pale faced as apposed to straight clown makeup and be more of a "comedian" at least that's what I've read in interviews.