I'm also in the same situation and I'm going with Big Ben.
Ben has been on fire lately, has the better matchup of the two (in my opinion) and stafford is a little banged up right now. Also what I noticed with Stafford is that he locks on to Megatron a lot and if he is not open, Staff tends to struggle. I noticed this in particular in the Atlanta game (I was at Ford Field), Atlanta focused on taking Calvin away and Stafford really struggled. It seemed like he didn't have much confidence in his other targets, as talented as they may be (Pettigrew). I think other teams are going to start doing the same and if Stafford does not adapt, I could see a drop off in his numbers.
Sorry for the slight rant but I think Stafford is on the decline while Big Ben is on the rise.
I think they will produce a very similar stat line this weekend but I'll give a slight edge to Big Ben - which is why I am starting him.
.5 ppr - 10 man league
Qb: Cam Newton/Tony Romo
Rb: Matt Forte/Marshawn Lynch/Benjarvus Green-Ellis/Stevan Ridley/Donald Brown
Wr: Jordy Nelson/Percy Harvin/Eric Decker/Brian Hartline/Kenny Britt
Te: Aaron Hernandez