Zax
HL and Neko byte code are equally platform independant, but I think you have to commit to 32 or 64 for Neko, you may also want to look at Cppia.
Cppia requires you precompile a core engine for the target the common case is NME toolkit and then the cppia script is read in, it is essentially a string that is translated at runtime, so I am unsure but I don't think it is platform limited. NME is a fork of OpenFL so you have a wide range of platforms although you could set it up with other platforms. Simplified code use!
cpp.cppia.Host.run(sys.io.File.getContent(inFilename));
What is quite nice for Android target which I have tried, you precompile the Acadnme project or grab it from google play put it on your android device, this is a precompiled core of NME and generic libraries then you can create your application locally and the application code is loaded up to the server from a terminal command in seconds and your application will run almost like a pure c++ NME application.
Hugh has a demo example use of Cppia with NME specifically for Android. But with NME it's fairly easy to run Cppia projects locally as well and it compiles very fast.
https://github.com/nmehost/acadnmeBut getting back to Neko and HL. In my opinion HL is kind of still a bit new I have no idea yet how to actually get the SDL etc... additional libraries working on my mac, on windows it's just a matter of downloading the prebuild, on linux I expect it's easier as dependancies are opensource generally linux so setup to work on linux but seem problematic via macport. Then HL 64bit is not complete so while HL is a better solution it's not yet mature. Neko has builds that run directly on android, rasberry PI etc.... or has had. But HL does not have aspects like threads etc ...
But with Haxe you don't have to commit to a HL, Neko or even Cppia as theoretically you can complie the same code to all of them, so you could start your setup with Neko and then switch to HL or Cppia. But normally you have to create some platform specific code, with Neko you often have a NME dll or OpenFL one or similar, same with Cppia, and stuff like HL SDL is platform specific cpp that you tap into. So it is only your user code that is really truely platform agnostic and that is only if you have a precompiled engine to run it as explained.
I am far from expert, I mainly just tinker with these tech, and I am sure Nicolas or Hugh or others can advise more deeply, truth is you probably need to make your own tests and read through some of the code examples etc...
Best
Justin