Thanks for considering Payoneer as your global payment solution!
We generally do recommend that you sign up through a site or company that you most primarily plan to use for receiving payments. Both in terms of usage fees and also available account services, this would generally suit you best - so a site such as iStockPhoto or similar.
You can of course receive payments from other sites to your Payoneer account, and aren't required to actually receive payments from the site you sign up with.
If you have any specific questions about the process, or concerns, feel free to ask and I'll be more than happy to assist.