I don't have my Leaf yet (on list for month of June), but I have the Ultra Motor A2B electric bike that runs on Li Ion Manganese battey chemistry, the same kind that the Volt and Leaf runs on, I believe. Ultra Motor's manual tells me to not let the battery pack sit empty for very long, and to top it off asap after I'm done riding it. It says frequent deep discharge is bad for battery longevity. It doesn't have the 80% rule like the Leaf does, but you never know, maybe its charger is designed to have a built-in limit of 80% already so they don't bother to tell you (like how it's automatically built into the Volt because there's no range issue on the Volt. Ultra Motor can't seem to stress enough in their manual that keeping it topped off is good and letting it stay discharged is bad. I've heard from other sources the same advice for LiIon batteries that is consistent with this as well.
I've had my A2B bike for 2.5 years now and I don't have any issue with its battery so far. I top it off every night, or every chance I get.
So I would vote for A, keeping my Leaf's battery topped off every night at 80%. Nissan never said anything about trying to not charge often. They only said to charge up to 80% for longevity. Option A fully meets this requirement.
On the other hand, option B (only charge every other day) means that you have more regular deeper discharges of that battery, which I think is bad for it. It also means that you unnecessarily limit your Leaf's range on days when they're only half full, not having the option to do extra unplanned trips if needed on those days. To me, the worth of the Leaf lies in its range, ready to deliver the full range (well or 80% of it) as often as possible. So to me option B basically cuts its worth in half on those days where it can only deliver half the range due to you letting its battery capacity run down to the low end.
If Nissan had deemed it beneficial to avoid topping off frequently, they would have said so already. Instead, the only thing they say is the 80% practice. It doesn't make any sense to assume that the 80% practice implies that frequent topping off is bad for the battery. You just don't want frequent topping off to 100%, that's all. And if range has not been an issue at all with the Leaf, I'm sure Nissan would have just built-in the 80% cap and not even bother allowing owners the choice of 100% charge. But range is an issue and there's value in leaving the option for 100% charge in, so they left it in.
But if you're reading too much into what they're not saying, you may end up doing more harm than good to your battery by letting it stay discharged more often than topping it off every night. Not to mention reducing the value the Leaf can deliver by not having a full 80% range available every day in case you ever need it.