383 or 318

Hello Folks,
I have a choice to put in a 383 or 318 in to my 71 Duster. (currently has slant 6) Which engine would you do if those were your only choice, and why? Im looking for advice, i have access to either. Cost is relatively the same, at least where i am. Obviously big block will /may have more of a "fitment" issue compared to the small block? Anyways, what are your thoughts?