Always look at the Ds you're playing. If RG3 is up against good rushing Ds, bench him. Big Ben is old but comes with Top 10 QB upside owing to his extended plays and Antonio Brown. Honestly, the Redskins offense is looking awful, regardless of them signing DJax. I'd steer clear of any fantasy player on that team.

Big ben is the pocket passer. Good for ppr. Rg3 is the runner, his upside is rushing tds. But injury prone

You should start RG3. There's always that chance that he can run it into the endzone, giving you more of an advantage.