I jump in it.
For now, Jones and Harvin are nearly a wash. Jones is with the better team and should produce more TDs, but he has to share targets with White and Gonzalez. Harvin will produce fewer TDs, but will make up for that by being the main target and playing for a team that should be behind a lot and throwing the ball more. Jones will probably score a few more total points and have bigger weeks than Harvin, but Harvin should prove to be more steady from one week to the next.
I've been on the Benson bandwagon this year, but I see Green-Ellis as an upgrade. Benson had great value in the draft as a late-round pick - as guy who's getting the bulk of the carries for his team and some goalline work, I see him as a better option than many of the time-share guys that were drafted ahead of him. He has been given the ball a decent amount this year, but you can hardly count on him in many instances because Green Bay would rather throw the ball and if they can win without running it, they will. Green-Ellis on the other hand plays for a team that does have some very good options in the pass game, but they need to run the ball to survive. I provided they are both healthy, I think Green-Ellis will far exceed Benson for touches and will outscore him too.
If you were being offered a time-share guy, I'd think twice about it. Green-Ellis is not in that situation at this point though.