I'm going to have to say the Space Marines would win, assuming equal number of men.
I think it's unfair to pit any faction against the space marines in equal number, 'cept for maybe the necron. Eldar technology probably surpasses even that of the DAoT, but have them face off against one another in equal numbers and the space marines will still probably win. The primary limitation of the space marines are there numbers, which means limiting the DAoT's numbers for the sake of giving the space marines an edge. Not entirely fair.