Keep in mind that opinions regarding companies vary widely (and wildly) EXCEPT where it comes to paying when payment is due. There have been ongoing issues with payments from Freeman Group--which supposedly are being set right but time will tell; Direct Scheduling Services (DSS) which I don't even know if they are still doing scheduling or shops; Goodwin, which may be cleaning up its act etc.
There are companies that pay very slowly, but still within their stated parameters. Habitually the last I see payment from include Service Check, Service Sleuth, Intellishop, but they still pay within their stated times. I had an issue with Informa about a November payment the other day that the delay is due to a late 'published' date, so I should see payment within the next week or so (no fault of mine but rather apparently an issue with the client). When a payment cycle is not met, I usually am on the phone fairly quickly to see why--but you have to go by THEIR SCHEDULE, not by what they usually do, before you start demanding payment.
Most companies are quite good about paying within the time frame they state.