I would damn near call it a wash either way. On the one hand you have a QB who routinely has high scoring games and a RB who will be part of a RB committee. On the other side you have a QB who is about 50/50 on good games and bad games but a clear cut #1 RB who rarely loses out on touches except for breathers. Since it is a dynasty you can also look at who provides better long term value. AP is nearing the twilight of his career, and with a strong RB pool shaping up for the NFL draft next year the Vikings may get his replacement. Brady is 39 but has shown no signs of slowing down. He retained his WR corp and added Bennett at TE. Dion Lewis will be back as well. Looking at the points per game from last year Brady was great for 90% of his games, Eli for about 60%, AP for about 80%, and Langford had a run of three or four games putting up big numbers but the rest of his games were single digit point totals. Osweiler put up pretty pedestrian numbers even though he was playing with two great WRs, and Eli is just as likely to put up four INTs as he is four TDs. All things considered, especially looking at your QB situation, I would keep Brady and try and pawn off Langford to somebody in desperate need of a RB.