Given the similarity in legal bases, which case has the best chance of success?
It’ probably the most prominent of the emergency lawsuits is California v. Trump, filed by California’s enterprising attorney general Xavier Becerra. (The last person to hold Becerra’s job was Kamala Harris.) Filed in the Northern District of California–part of Trump’s least favorite judicial circuit, the Ninth Circuit–the case probably has the highest profile of the four.
On the other hand, one issue that distinguishes the cases from one another is the matter of standing. To file a lawsuit, parties must show that they are individually harmed by the action at issue. In a controversy like this one, obviously the main conflict is political, but that’s not the same as a judiciable matter for courts.
In the California case, the states argue that they are harmed by the diversion of resources to the border wall. But because of Trump’s recourse to military budgets, that’s actually a hard argument to make; it’s not clear that the money for the wall is being diverted from money that would otherwise be spent in New York or Massachusetts.