They pretty much do the same for most champions who would use them, at least for ranged carries, may be slightly different for melees, but not much.
PTA gives you burst after 3 AAs, and some damage after. Hail of Blades gives you burst for your first 3 AAs. So they both add burst, with PTA adding DPS as well and Hail of Blades being entirely frontloaded.
However, if you want Hail of Blades as a ranged carry, you also want Stormrazor I guess? Meaning you also want Statikk most likely.
Even if you build pure AD otherwise, those alone get you to ~2 AS already, not including the AS steroids most champions who would most likely use this have anyway (Draven W, Quinn W, Twitch Q ect).
So while you can surpass the AS cap with Hail of Blades, you also have enough AS to almost instantly proc PTA.
The difference here seems pretty insignificant to me. It just becomes a matter of which one is better in most cases, which one kills someone faster.
Maybe it's just about the stats, and someone like Draven actually just takes Hail of Blades + Sorcery or something and ignores AS otherwise, and maybe I am wrong and you don't even get Sormrazor and just build pure AD/Lethality?
But really, what is the difference between PTA Draven and Hail of Blades Draven? PTA Draven most likely attacks you 1-2 more times, and builds one more AS item or something, while Hail of Blades Draven kills you with less attacks, but those do more damage each, because he builds no(maybe one?) AS items.
Sure, it changes build and rune combinations, but the playstyle and end result are the same.
But overall those two seem too similar.
Let's say I'm Quinn and my build is something like Stormrazor, Statikk, LW, Duskblade, Ghostblade.
Even if they make Duskblade and Stormrazor exclusive, it would just be a PD or Death's Dance to replace it, maybe that's correct anyway.
What I end up doing is flying up to someone and attacking them really quickly for ~2-3 seconds, with one giant attack at the beginning.
This doesn't change much with my Keystone.
In the case that it's a carry, I will kill them with 3-4 AAs anyway, and my AS is already at 2.5. What is the big difference to doing the same, but with 3.5 AS instead? Maybe I need 0.3 sec longer to kill them? Wow what a difference.
If it's someone with more tankyness, then what kills them faster? Let's say with Hail of Blades I need 10 AAs, then that takes me about 3.5 seconds.
Let's say with PTA I only need 8 or 9 AAs, then that takes me about 3.5 seconds as well.
You can do this for 15 AAs, 20 AAs, it doesn't change much. Maybe one or the other is half a second faster, it barely matters.
And they are really similar earlier on as well.
Both a used in lane for quick burst with short CD. One has 5 Sec but needs you to go out of combat (also minions), and one has 6 seconds per target, but doesn't need to you to go out of combat.
Yes, Hail of Blades is slightly easier to use, since you essentially get the damage right away, and PTA gives you more DPS (especially in teamfights and duo lanes), but in the end they are both used to kill someone fast with a few AAs, which one you use just depends on which one is more optimal. You get more AS? Go PTA. You get more AD? Go Hail of Blades.
Such deep decision making, and such different playstyles.
Sorry this all is a bit incoherent, it got longer than I wanted to it. I just kept changing the way I tried to make my point over and over again, I hope my meaning still comes across somewhat, maybe I will take the time later and rewrite it to be more coherent.
Also, maybe you agree that they are very similar, but don't think that is a problem?
I would like to hear everyone's thoughts on this.
I think they support almost identical play patterns, and it will just end up depending on what build + rune combination kills someone faster.