I wouldn't necessarily compare any of these options directly against one another (including the NOX). I get the desire to do so certainly, but it's hard to compare a 320 unit at $2500 and 640 unit at $4500. Obviously there are similarities in the application, but maybe the better comparison is the Breach to something like the ML19 just due to price/performance being a little bit closer. The MH25 is going to slay the Breach in most things except having onboard photo/video. But it's also essentially double the price when you take into account the eyepiece upgrade you're most likely going to want to maximize the investment.
As for the NOX I'm not sure that is very comparable either considering it is weapon mountable as well and therefore more of a 'jack of all trades' rather than an application-specific unit. It is inherently not going to be as good as a pure head mountable unit in some ways, but gives the added value of providing a weapons mountable platform (an area where it will also be outperformed by certain dedicated weapon mountable thermals designed solely for that purpose).
If your application is going to be head mountable, I'd let your budget drive the question with the understanding that the FLIR will take you part of the way to the MH25's performance, and the MH25 is the current king. The ML19 might be in between, no experience really with it specifically. If spending even more than the MH25 to get access to a different application set with the NOX is of value to you because you don't have other weapon mounted thermals already, then let that be your answer!