Thomas: Certainly capable of having a good game, but I don't see him as a reliable fantasy option given that 1) he's splitting time with Ingram and Sproles and 2) Drew Brees still has Graham, Colston, Henderson, and Moore catching his passes.
Gerhart/Turbin: You could consider one of these guys if Peterson or Lynch is ruled out, but the Jaguars and Cardinals both have solid Ds.
Williams: Tampa Bay's planning to be a run-focused team, and Vincent Jackson, Dallas Clark, and Preston Parker could all vulture targets from Williams. Plus, I'd give Freeman at least a week to see how he bounces back from last season. I've read that the Bucs are growing more concerned about his accuracy issues.
Little: If the Browns game plan is to attack the Eagles' LBs and safeties, that sounds like a recipe for a lot of Little. Big risk is whether he and Weeden have been able to work through their timing issues.
Fleener: Bears D got roughed up by tight ends last year, and he obviously has the chemistry factor with Andrew Luck. Decent chance he'll get in the end zone, IMO.
Keep in mind that Seattle has a later start than the rest of the games, so if you plan on going with Turbin but Beast Mode ends up being active, you'll be pretty much SOL.
In your position, I'd probably go with Little or Fleener, but neither of them is any kind of lock.