I personally found Heroes vs Villains to be the most consistent and generous gametype for XP.
A mediocre performance would bring me approximately 10,000 or so points, a better performance has seen me earn between 18,000 - 22,000. Converted into credits will see you earning around 400+ a game.
There currently aren't any methods of boosting for this trophy, but progress towards it can be comfortably tied in to most other online trophies.
Good luck!