I would just hold Ridley. He's good. He is going to get EVERY team's #2 corner. Sure, his ceiling is limited due to Julio, but the ATL pie is pretty big, Freeman is a shell of his former self, and I wouldn't worry about Sanu or Hooper much at all. Yes, he will have some stinkers, but all WRs have them (even the elite WRs).
In fact, ATL having Sanu and Hooper and Freeman, along with Julio, pretty much insures Ridley is getting single coverage.
Now if you can sell Ridley plus a piece and get an elite player in return, sure, cash out. But I think Ridley is a player that you won't get full value in a trade.