If I was going to trade any of the three, it would be Barber. That said, I wouldn't do it straight up for MJD, and would want additional compensation. In a PPR it's debatable which of the two would have a better year, but MJD is obviously still in a full committee and I would think his owner is somewhat frustrated by Taylor's presence, and would jump at the chance to trade him for a "starter". Barber is also most likely to break down, and his perceived value as of today is probably higher than his actual value. Felix Jones is no slouch, and the Dallas staff is smart enough not to hand him 20+ carries a game consistently.
Lynch and Gore have great situations in that they have little competition for carries and will remain their teams focal point on offense. Especially in Gore's case, it looks like he stands to catch a lot of passes this year. You'll definitely want to hold on to him in a ppr.