If you built something useful and high quality , I think CodeCanyon would be the Most STEADY one , when it comes to continuous sales.
Take a look at Envato’s own graph:
http://notes.envato.com/milestones/the-envato-marketplaces-population-3-million/ Do the math (pageviews x average item price) probably isn’t a bad estimate of relative profit. ThemeForest is crushing the other marketplaces.
Also, take note: the bar chart is a total lie. The numbers tell a completely different story of which marketplaces get traffic.