I can't really say which is better.
Open Box -
Positives : Only one owner; structurally-speaking, an original item (wasn't constructed from a bunch of parts lying around).
Negatives: possible cosmetic wear and tear (not much, but still possible since it was opened at one point); components from the box could potentially be missing (a manual, a cable, etc).
Refurbished -
Positives: Aesthetically-speaking, item is in mint condition. They never allow worn-out looking items to be deemed "refurbished"; usually a better discount when compared to an open box item (even though you said assume the same price); always comes with original accessories and manuals no matter what; hasn't been registered.
Negatives: Structurally-speaking, it *could* be an item thrown together from parts lying around, so the quality of the item is comprised for a like-new appearance; greater chance of item failure due to construction - even if the item wasn't built from spare parts, the original item more than likely had an internal component that needed replacement.
In the end, I'd probably choose refurbished even with the possibility of a product failure. Why? Because I'd extend that 1 year warranty to three years under Apple - and I'd be set.
Correct me if I'm wrong - but even on a refurbished product, doesn't Apple always replace the battery?