For most of this shortened free agency period the Jets have been the leading candidates for Asomugha. Most of the momentum has been swinging in their direction because of their head coach and players.
Rex Ryan is a guy that many players want to play for. They love his confident attitude and the knowledge that he knows how to win. The players help the Jets' case because some of the ones with higher contracts like Mark Sanchez and possibly Darrelle Revis are willing to re-work their contracts just to bring someone else in who requires some more cap space.
If Nnamdi is looking for a team that can win a Super Bowl in the next few years, New York is the place for him. The offense has a great running game mixed with an average passing game. The defense will be even better if it has the two best cornerbacks in the league and would shut down most offenses.
If Nnamdi is going to be like Antonio Cromartie and follow the dollar signs, then San Francisco is the place to go. The Jets still have a few more players to sign and will not have as much room for him as the 49ers will.
As to why he will go today; negotiations will continue to heat up between the two teams and Nnamdi. What will add to the pressure is that training camp for these teams is essential and they will not want him to miss a single day.
Of these two teams that will probably land him, the Jets have the edge. With his addition they will have a championship caliber team. They have one of the most liked coaches (liked by players) and a team hungry for a world title. It will be an interesting 24 hours to see who lands the number one free agent but either way, he is going to a team on day four.