As for Niese, if he's traded, a remote possibility now, I believe he'd go to an AL team.
Why not the NL?
Well for one, the Dodgers will probably land Hamels or Cueto-who knows with their deep pockets maybe both-and as for the Cubs it wouldn't surprise me if Samardjza goes crosstown to the northside for a return engagement. The problem with the NL is that most of these teams in the playoff chase don't have glaring pitching needs. Also, Niese is probably your 8th or 9th option in a trade with people like i mentioned being available as well as Latos, Haren, Kennedy, and possibly Buchholz and Kazmir. I'd add Shields to that list as well.
Speaking of Shields, if he does become available, the Cubs could make sense there too. I can't see them getting a pitcher for the stretch run without parting with Baez at the very least.
Getting back to Niese though. The AL has a lot of staffs in need of arms: Tigers, Twins, Astros, Jays, O's, among others. So let's indulge in some conjecture and see where Niese could land in an AL trade.
Orioles-If Matusz steps up they would already have two southpaws in the starting 5, but if he falters, then Niese would make a lot of sense here.
Blue Jays-Buhrle is their only left starter so Niese would be a good fit. After getting fleeced in the Dickeey trade who knows if Anthopoulos would trade with the Mets again.
Tigers-Niese would be a huge upgrade over the revolving door they've had at the 5 spot this season.
Twins-Nolasco is out and Big Pelf is imploding so the need is there. He could be a nice compliment to Milone on the portside of the Minnesota rotation.
Royals-Gutherie has been a disaster and Duffy a disappointment. Losing Gordon puts more pressure on KC pitching. Niese to the Royals makes a lot of sense.
Astros-The back end of the Houston staff has been shaky. Niese would make a nice addition to the rotation not just this season but long term. Houston has prospects to trade and is the surprise team of the season. They will probably be players for the bigger deadline pitchin names but this might end up being the most logical destination for Niese.
The Matz injury may make this a moot point but with this team...who knows???
Should the Mets keep or trade Niese? If not, why? If so, who do you think makes the best trade partner?