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I used elance, then it became upwork. And I recently used freelancer.com. I've used fivver for some small book promotion.

Yes Elance was great, had the least % fee from the job. oDesk and Elance were the two biggest ones, then Odesk bought Elance and changed the name to UpWork. I find that there are better platforms whether you want to hire or find work. Fiverr for hiring, UpWork for finding work.