I have worked as a freelancer as well as contractor on upwork. It is a good platform to find quality freelancer in a budget. You can also 99 Design which is basically a place to find designers and web developers.
I have only used upwork. However, screening process is tedious. Every Tom, Dick, Harry applies on your job and it is really hard to find a good fit. The applicants do not ever read the job posting closely. I joined Fiverr recently and I am yet to hire anyone on Fiverr.
Attention: "role based name" email prefixes such as support, webmaster, info, contact, forum, service, affiliate, admin, traffic, partners, marketing, etc., for our member accounts are not permitted. They are acceptable for a vendor listing, but not for the member email. This is due to bulk email processors scrubbing them for delivery due to extremely high bounce rates. Please apply for membership using a personalized email prefix. Something like firstname.lastname@example.org.
If we discover you signed up with a role based name we will give you only one message to change it. After 3 days your account will be removed if the email is not changed.