Both Stevan Ridley and Shane Vereen had big games Week 5 against the Bengals, who rank 27th against the run. They may not be so lucky Week 6 at Buffalo. The Bills rank second against the run, allowing 71.0 yards per game and 3.0 yards per carry, and have yet to surrender a touchdown to a running back this season.
Because the Bills are more vulnerable to the pass than the run, Jamey Eisenberg actually prefers Vereen to Ridley this week, though for my money, Vereen hasn't been productive enough as a pass-catcher this year for me to make that distinction. Ridley got three times as many carries as Vereen in Week 5 and was on the field for about 15 more plays, so if you're going to start one, Ridley is still the way to go.
I'm just not sure either is so advisable with this matchup. As Chris Towers pointed out earlier in the week, the way the Patriots use their two backs can vary drastically based on the way the game is going. If Ridley isn't a sure thing with a favorable matchup, surely he isn't for this one.
That doesn't mean he's an outright sit for me. Enough high-profile running backs have been lost to injuries the last couple weeks that he may still be your best bet. I just wouldn't go out of my way to start him based on last week's performance.