FA14 is a big step up from FA13. Apart from more/improved visuals, the textual side of it is a lot better. After the errata overload in FA12, more thorough steps and cycles of review have been taken to cut down on the errata for FA14, which hopefully have been kept to a minimum.
I would say if your FA13 is already heavily annotated, sticking with it is fine because it's still a solid text, but if you're a fast reader and can make time for an additional pass before your exam, you'll notice some interesting factual updates that might bump you up 2 or 3 questions.
Good luck,