When choosing a player, I think it should be considered the talent of the three teams.
What are the weaknesses of the Bears, Vikings and Lions? I don't think Cullen Jenkins makes any one of them three that much better.
With that line of thinking, I'd have to choose James Jones. I think James Jones makes a bigger impact than Cullen Jenkins, even though Cullen Jenkins is the better player. Lions, Bears and Vikings each have stout DL's already, but the same can't be said about each WR core.