I've hired a lot via UpWork and consider it the lesser of evils among these platforms. It is still all kinds of evil, though. I've heard it's at least as bad for the contractors.
I find Upwork seems to give people high summary ratings and when you look at their history and there is a bunch of bad reviews. There is something dodgy going on there which is a main reason I flipped to Freelancer. That and I thought it was good to support a company from my country.
However there seems to be an agency mode on Upworks which might be similar.