As promised, I shall outline the various differences between FAir and BAir during their discussion period!
The new animations are so good imo, even if it comes with the lengthy end lag.
Data tables:
Now, to focus on each specific difference:
Hit-frame : FAir (F9) / BAir (F6)
Like in every other iteration, Zelda's BAir hits 3 frames faster than her FAir. While 3F is still only 3/60 of a second, 3 frames can be very noticable for hit-frame differences in smash. Aiming with FAir and BAir are very different things, you often need to be closer to the ground in most cases when using BAir. BAir's earlier hit is also more advantageous in aerial combat. While niether is very good in aerial combat. BAir's quick hit can make it easier to get the sweet-spot out when you're finally close enough. It also gives it easier retaliation factor under the rare circumstance you can use it to retaliate against a weak hit.
Hit (Sour-spot) duration : FAir (5F) / BAir (4F)
Probably something far less noticed is that since Brawl, FAir's sour-spot lasts 1 frame longer than BAir's. In the grand scheme of things that's pretty insignificant, but...It's there! :D
FAFs and end lag : FAir (FAF: 53, end lag total: 40F) / BAir (FAF: 53, end lag total: 44F)
So, another interesting thing that's brand new to SSB4 is that FAir and BAir actually have the same FAF (First actionable frame) but since FAir hits later and lasts a little longer, this means that BAir actually has longer end lag than FAir. I guess the idea was to tradeoff the earlier hit-frame for a few more frames of end lag. The difference isn't very big, and since their FAFs are the same now it won't feel like too much of a difference.
Auto-cancelled landing windows, and landing lag : FAir (AC: 1-3, 50>, landing lag: 23F) / BAir (AC: 1-2, 52>, landing lag: 25F)
So, once again a small but odd design choice that I consider the tradeoff for the stronger sweet-spot (See: KB stats.) where, while both FAir and BAir have rather bad AC windows and longer landing lag, BAir's AC is almost non-existant, and it has 2F more landing lag upon non-AC'd landing. You may feel it a little in gameplay, and once again combined with FAir hitting later/longer, then BAir has notably worse frame data there.
Bone numbers : FAir (7/5/3/7) / BAir (11/9/3/11)
This very pretty much only noticed when looking at the numbers, and has NO effect on gameplay. But I list it anyways.
Sweet-spot KB stats : FAir (24/95) / BAir (28/96)
As more people might know by now since I bring it up a lot, BAir's sweets-spot is slightly stronger than FAir's. I really don't know where Sakurai originally got the idea in Brawl to mkae this a thing, but it is. So going for BAir will reap you a better reward, even if it does have more lag overall.
Facing restriction : FAir (n/a) / BAir (Only hits the direction opposite to Zelda.)
This is another new to SSB4 and unique to BAir trait. When you hit with any hit-box on BAir, it will ONLY, hit backwards relative to Zelda, In contrast to FAir, which, if you hit with the inner most hit-box from the wrong side, will send them backwards relative to Zelda, but it will send forward under regular circumstances. The difference doesn't have a big effect on gameplay. I don't know why they only applied a direction restriction to BAir, tbh. Maybe it only fit well in Sakurai's opinion with the BAir animation.
That outlines all of the data differences between FAir and BAir! The differences between the two really end up balancing the two in a way. I'd say BAir is just a little better than FAir, since it KOs roughly 4% earlier, can hit closer to the ground, as well multiple BAir "techs", such as SH AD BAir, and ledge trump BAir (And Dthrow reads being easier and better with BAir.) and the tradeoff is that since in most cases you'd probably be using it and landing lagging anyways you'll only have 2 more frames of end lag, which is pretty small.
Overall I'd rate them a 2.25/5 they are undoubtedly flawed but really powerful (like, kind of fraudulently sometimes.) and fab and awesome! <3