It's the Rock easily for me. Look at his resume for starters...how many of these fighters could Joe realistically beat? For me, Rocky pressures and walks Joe down, getting some peppering for his trouble and ends up stopping Joe.
People forget that Joe has decent power - dropping Eubank (pretty decent chin lets not forget) not enough to stop Rocky, but hard enough to at least get his attention.
The fact that this thread still persists is embarrassing. There is just no rational argument for Calzaghe. None. Marciano would give Joe a sustained beating. This is not really a slight to Calzaghe since these men were not in the same weight division. But, this thread is a slight on the intelligence of reasonable posters.
Ironic, isn't it, how you keep it going with your post here, haha! Sorry you find my posts a slight on intelligence