C2 has limitations with exporting to android, I can't get games that are simple to run over 30fps on a samsung galaxy 4 tab. Even though I'm a C2 fan, limitations of C2 are or will be greater, considering the future of what both will become, unless C3 has something incredible planned I just don't see UE4 being the lesser choice in the near future. Plus there are consoles to consider. Nintendo sure, but currently they are mostly off limit and will probably remain so for some time.
Really though, I'll have to investigate more, not really sure how exporting works for HTML5>Android with UE4, for me that will be a deciding factor.