^ FFI has a 'storyline' insofar in that it strings everything loosely together for the purpose of a coherent adventure. Really, it's more of a vague plot than anything, and one step above non-existent. XIII's story is... well, more elaborate. Comparing it to FFI's story 1:1 is really rather silly, considering one is an HD game and the other is one of the first 8-bit NES RPGs.
As far as individual games go, FFI, I contend, is the better game. Just for 'story' reasons, I'd go with cute little FFI rather than sit through XIII's monstrosity masquerading as a plot a second time.