My vote is for Haxe :)
Summary: depends on your specific needs and where you fall on the security/freedom threshold. Do you have some more specifics about your project rather than just comparing the two in the abstract?
(Also as josefiene pertosa pointed out to me on twitter, you can use Haxe's C# target in conjunction with Unity so the answer can easily be "and" instead of "or")
It is my understanding the Haxe to Unity arrow is one way ie Unity does not support Haxe
I will give you the specifics when possible :-)