>>2321246The movie is shorter, intended for one sitting viewing, unlike the OVA. It has scenes not included in the OVA that put a different spin on the story.
The OVA is more ambiguous, with some events off camera, or open to interpretation. The movie is very clear, for better or worse.
This Anon liked the OVA better. I've only seen the movie twice, and I've seen the ova at least a half dozen times.