Trendsource is a reliable payer. So are Ipsos, Kinesis, Confero, Maritz, Merc Surveys, A Closer Look, SeeLevel X, and Alta. There are many more that will pay on time and without having to chase payment, but those are a good start.
Do a search on "chase payment" to find companies that often need to be "asked" to pay their shoppers.
"Let me offer you my definition of social justice: I keep what I earn and you keep what you earn. Do you disagree? Well then tell me how much of what I earn belongs to you - and why?” ~Walter Williams