Upwork is better than Freelancer, at least on a UX level, Freelancer's site is a mess, I'll concede that. However, Upwork will arbitrarily lock your account and you will have no recourse, so don't put all your eggs in one basket.
Once, I asked Upwork technical support about an issue I had where they were showing the wrong hourly rate to clients (who asked me why I was changing my rate), and I asked Upwork whether it was possible to resolve, very politely. They told me no, that's just how it works, it won't be resolved. I was totally baffled, but what can you do? I would just continue to explain to clients the problem.
Upwork, after a support issue, gives you a little survey "did this resolve your problem / how satisfied are you" or whatever, so I put no, and unsatisfied, obviously.
Not 30 minutes later my account was locked, so I could not apply for new jobs, nor withdraw any money that already belonged to me. "It needs additional identity verification", despite having worked there for a long time, having 100% positive feedback, all jobs successful, my photograph on there, all forms of ID they initially required were provided, all payments successful, contracts ongoing, etc. I had to install some nonsensical app and have a webcam interview to prove I'm the guy in the photo, etc. It seems entirely too coincidental that I would give a support person a bad review and then be flagged immediately.
So, if Upwork asks you for a survey, beware, you are obligated to lie. I have been using Upwork since then, but at least now am aware of and prepared for it to be locked up or deleted at any time.
Upwork charges 10-20% of an enormous global tech labor market and there is no major competitor? Freelancer is garbage and I've heard horror stories about Toptal. I'm open to suggestions, and encouraging some enterprising reader to start a competitor; I'll use your site.