I would go with Lynch due to matchup. As for Blackmon and Austin, well Gabbert was awful last year, this year he can only go up and I know it's only one game, but him and Blackmon seem to have something building. Austin is also battling injury and although he is apparently supposed to be fine for week one, I think the gap between Blackmon and Austin might be closer than other think. Depending on what amount of players you start at each spot, I might consider putting both Austin and Blackmon.
The other thing to consider here, is that the Cowboys play the defending champs. It may not matter so much here, but in every game since the NFL started having the defending champs in the first game of the regular season, the champs haven't lost.