Well the "source" is arguable. If you want stock parts it's definitely Mouser (or their suppliers) but if you want a project, namely something new made out of parts provided by Mouser then it's still CrowdSupply. I didn't take the time to compare but I imagine prices are roughly comparable and maybe you get projects slightly faster on CS, I'd hope so at least. You definitely get to follow the evolution of the project though, which is positive (your learn how it goes) and negative (you can get frustrated by delays).