Characters like or similar to another, but not always in the same era, work best.
'Rambo Vs Terminator' is right up there with 'Batman Vs Predator' and 'Superman Vs Terminator'. I always thought that the Supes vs Terminator comic would be like one page of:
Superman confronts the Terminator - Terminator shoots - Superman scrunches Terminator into a small ball of metal - THE END.
Match ups are popular as people want to see how each character performs against another - which is fair enough - but more than often, in a film, its obviously just another person's opinion of how they would perform against each other and the circumstances that draw them together.
As divided as we are here about the AVP films or FVJ (Freddy vs Jason), they had the established base audience large enough to warrant film versions.
Although I'd like to see a decent 'Robocop Vs Terminator' film I don't think the audience for that film is anywhere near what it is for AVP or FVJ.
Besides, I'm more intrigued at the moment by the idea of Ash (from the Evil Dead series) going up against Freddy and Jason. The comic book series is out already, perhaps that will expand the fanbase to a point where we'll get the film?
Its strange, he's the only horror icon I can think of that's a 'good guy' - and I suppose that destroys any suspense as to who would win in a film version I suppose.
My four contenders are:
Antonov Navarre (Ladyhawke) - Skilled, resourceful and righteous.
Ash (Evil Dead 1,2,3) - Overconfident, skilled and determined.
James Bond - Skilled, intelligent and tactical.
Conan (Conan The Barbarian) - Ruthless, skilled and powerful.
I was going to put Roy Batty from 'Blade Runner', but he's a replicant and as such superhuman to a degree.
When I say James Bond I mean the Dalton/Brosnan/Connery type, not Moore's wise cracking 'adventure hero' type. lol!