If its pure fantasy movie ideas, the the ninja would always win. Here's my logic:
If the Japanese make the film, then of course it is going to be the ninja that wins.
If the Americans make the film, then the SAS man can't win, because that would require the American film makers to acknowledge that us Brits have the world's most elite fighting force and not them.
If the french make the film, the ninja will win because despite being our closest foreign neighbour and official friend, the french don't particular like Britain.
So what if the British make the film. Well, our war films tend not to be all gung ho glory and victory like those that emerge from the Hollywood movie factories. British made films tend to be much more gnarly, nitty gritty and no polish, so it would have to be about the hardship that our hero suffered and his bitter struggle but ultimate demise.