TL;DR UpWork has itโs problems, but you can find great clients and freelancers on it.
Iโve been on UpWork (formerly oDesk) since 2009. Itโs been great for me! I also signed up on Elance in 2010, but I was never able to land a job there, so I stuck with oDesk/UpWork.
There are many people, freelancers and clients, who have issues and bad experiences on UpWork. However, my view is that itโs an international marketplace, and it will therefore magnify the best and worst of freelancing - youโll have good clients and bad ones, great freelancers and poor ones. A failed project, or a bad experience isnโt necessarily an indictment of the platform.
That being said, the merger of Elance and oDesk into UpWork has been fraught with technical problems. Personally, Iโve had no issues whatsoever on this platform but I will not discount the fact that other have had issues. However, the people who manage the platform have accepted that there are problems and are working on them.
Overall, I think itโs a great platform and you just have to make it work for you.