I was playing against a ZSS (good one too, shoutout FK if you ever see this) this weekend. He beat me, unfortunately, but I think it was primarily due to me not knowing the matchup very well (and a suicide). Nonetheless, the guy was good.
Main thing that was hurting me was that I couldn't get the chaingrab. He consistently used ZSS's downb to escape it. I know ZSS can be chained (so I'm told, at least), but I couldn't make it happen. I ended up just doing a d throw to DLX for around 30 dmg. It isn't bad, but I'd much prefer to get 5 throws in.
Is the timing just different for ZSS? Do you have to walk? I was just dashing.
Anyway, from my limited experience:
ZSS has a great startup projectile that has a lot of knockback and does a good amount of dmg. I watched my friend's Marth get wrecked first stock every time because of this, and he couldn't comeback from it*. Luckily Falco has a reflector, which you'll probably use more than usual during the first stock. Also, in general you'll be using your reflector here more.
ZSS has very limited approach options here and you should flourish anytime she has to approach. SHL/SHDL across the stage makes it rough to do much but crawl at you and you can either IAP or reflector her. Her dash attack is usually predictable and you can usually make her eat a reflector.
Best thing about this fight for Falco is that he can effectively force ZS to fight him up close. Falco isn't the best up close fighter, but he is significantly better than ZS. And most of her stuff can be shieldgrabbed to start the chain.
Falco can't spike very well at all. I landed a strong spike at high percents TWICE and she managed to recover using the tether recovery. It is easy to spike their down-b if they use it close to you.
One strength ZSS has against Falco is Falco's glaring weakness: recovery.
Phantasm is typically the best option, we all know Firebird's weaknesses. Phantasm is predictable and can be hit through her Bair. So be careful. Trick her into trying to ledgehog you and go back on stage or vice versa. Also, watch out for an off the stage sideb, the range is ridic and it really strengthens her aerials.
Also I like to phantasm a lot in this matchup to reset spacing and force her to approach.
And her sideb does outrange your reflector (unless I'm mistaken), but only by a very small amount.
Anywho that is all I got for this. Someone more knowledgeable should chime in. I don't know enough to assign the match an arbitrary number, but I think Falco has an advantage,
*He now knows to just counter and throw them off stage, but he didn't then.
ALSO: Can someone confirm/deny ZSS's downb getting out of chaingrabs?