I've tried PFF, PFN and TDN simulators. They all have their strengths and weaknesses.
PFF is all predicated on what they think the rankings should be rather than what they most realistically are.
PFN's trades aren't that realistic and their rankings are a bit mixed.
TDN has the best rankings (they actually have scouts who work like team scouts) and their trade scenarios are good when they work. But it's a pay site to access the trade function. And there are glitches in the trade system and it will glitch and auto pick for you when you're on manual.
It kind of depends on what you're trying to do. Are you playing to create the greatest and most unrealistic haul or are you trying to create a realistic outcome?