I'll take Nelson over Gordon by a lot, redraft or dynasty. Nelson should have several years left of high end production. Gordon is younger, but that doesn't mean he has more years left. He might never play again. He might play this year, get millions when he's up for free agency next summer and go on a bender to celebrate. Can he play more years than Nelson? Sure. But you gave to discount some of those years, so it's not the huge advantage you'd expect.
Nelson had several years of stud production, but will be a year removed when he comes back. Gordon has one, and will be three years removed when he comes back. Guys like Braylon Edwards, Brandon Lloyd, Michael Clayton, that other Tampa guy, that other other Tampa guy - lots of guys have career years then drop off the map.
The Packers learned this year that Nelson is the straw that stirs their drink. He's the main man for one of the great qbs in NFL history. When Gordon came back he was supposed to be the number one guy but wasn't. There were definitely extenuating circumstances, but the fact is that his talent alone wasn't enough for him to instantly dominate, which means we need to see if he puts in the effort that an elite player needs to put in when he hasn't done that in three years. It's not like he's surrounded by role models in Cleveland. Will he put in the effort it takes to become elite?
Jordy stays in the same offense with the same coaching and same qb, all among the best in the game. Gordon went from a vertical offense to Hue Jackson's run heavy offense, we still don't know who the qb will be, and we don't know how Gordon will fit.
There's risk with both. No doubt. And everyone loves young players with upside. Long run I still think Jordy is the much better play.