I would recommend joining Gigster or TopTal if you can. Both services are in a completely different league to Upwork in all regards — great clients and projects, high-quality work opportunities, money.
I freelance for Gigster, so I know more much more about them than I do about TopTal. The business models the two companies operate are different. From what I understand, TopTal connects the workforce with customers on a long-term basis, and the pay is per hour, while Gigster allows freelancers to take several gigs at any given moment and the pay is typically set according to the scope of work and the dev’s reputation. With some very rare exceptions, all work is remote.
So far, my personal experience with Gigster has been amazing. I have worked on a variety of projects that have really helped my resume shine to shine, I've met lots of cool and friendly people (many of whom are among the best in their field), and I've earned quite decent money in the process.
Many Gigsters have a stable six-figure income. While this may only scratch the surface of what people are paid in the Valley, when you think about combining it with the freedom to live/travel wherever you want — be it in Thailand, Costa Rica or Greece — you get a true perspective of the potential of joining Gigster.