Nash should go to NY or the Lakers. He'd make a big difference and start for those teams.
Yes he would... but only on the offensive end. NY's problems are not on the offensive end, but on the defensive end (obviously). NY would still be a first-round exit playoff team with Nash on it. It is for this same fact that I think they would be stupid to sign Ray Allen. At least D'Antoni is gone though, that guy is horrible.
As for the Lakers, their Achilles heel has been the inability to defend (and produce from) the point guard position. The Lakers were an improved defensive team under Mike Brown last year, but look for that to regress if Nash gets significant minutes.