Freelancer is the best when it comes to running a small agency and getting as many jobs as you can, and gathering international experience and reviews. It is also quite good for earning small, extra money on the side when you have additional free time for doing smaller time-scoped projects.
Complex interface: tracking your freelancer's work status is harder than it should be. Tracking sometimes does not work as it should.
Mobile app is laggy and sometimes glitchy so personally I prefer to use the web-based platform (inconvenient for someone who is traveling on business trips a lot).
It is hard to find quality talent for simple tasks (translation). It is easy to find talent for technical tasks though (iOS app developers for example).
Of the freelance hubs I am listed on, more than a few, I haven't been as successful on Freelancer.com. Freelancer.com, I think, could use some more development and better customer service. It does separate itself with its competency tests, but I'm not sure this is enough. Still, I check out the project lists from time to time and keep my profile up to date, just in case