I loved reading this entire post, and thanks for the time and effort to not only extensively test on your own but also post your findings on my guide!

Subtlety definitely has a large drawback in that you need to wait a whole 4 seconds to get the bonus Energy Regeneration. However I feel that Vigor's bonus Energy Regeneration of only 2 is a bit low and wish it was buffed (or Subtlety's downtime was reduced to 2 seconds). The option comes down to your preference and the enemy team. If you are facing multiple Heroes with Reveal mechanics, then Subtlety will be by far the lesser choice of the two.

As for the builds you came up with, I was looking into a large combo build with Cold Blood and Expose Armor to deal high damage within the Expose Armor window. It required just as you said, a period of rest after your opener to get enough Energy to use the entirety of your burst with the bonus 25% increased damage taken from your target. However, that is quite a bit of time that your target has to prepare for the incoming burst, whether it is lock you down and kill you first, run away to escape, or seek help from teammates. Once again it will depend on how the enemy team is set up and how they group throughout the game.

I built the SS build to be so dependent on Stealth to perform well while still dealing damage (as opposed to the TF build). While opening with Garrote is the way to get the highest damage output, the Talents amplifying Sinister Strike's damage is enough to kill most of the lower-Health Heroes that are Valeera's prime targets.

Stealth Heroes are very dependent on Stealth, and as such deal amazing amounts of damage. However counter that Stealth and you take away their biggest advantage. I suspect Quick Match to be full of Tassadars, Rexxars, Chromies, and Brightwings when Valeera hits the live servers just as it is now in the PTR. It will take time for the Quick Match meta to calm down from the anti-Stealth campaign it will be on, but this will be a great time to explore Valeera's strengths while not in Stealth. Obviously I need to test my builds much more extensively, and I hop to tweak my current ones to not only fill the role I want them to but also be able to do it, at least, to a minimally lesser degree. One strength of Valeera is that Vanish provides 1 second of Unrevealable, so timing a Vanish into a quick Cheap Shot or Garrote mid-fight is going to separate the new players from the experienced.

I'm just going to apologize here for the massive blocks of text...

EDIT: Just going to preface it here, everything that I mention here was DONE IN TRY MODE as it took over 30 minutes to get into a single match with and against other players.

Just tested it out in Try mode, and against the Bruiser Camp if you Blade Flurry all of them after applying your poisons, it will inflict the poisons on all of them. I also just realized that you can have both poisons applied at the same time... slow + reduced healing received.

Though I think taking Crippling Poison would be a somewhat niche talent to choose. Not having Vigor or Subtlety really hurts Valeera's damage output, so I think that Crippling Poison would probably be best if you're with a team that will actively work together. Otherwise I think taking Vigor or Subtlety will be better if you're just going solo and you find yourself in an uncooperative team.

In fact, I think her poisons make her much more so a supportive assassin that helps other heroes that may have more burst or sustained damage to kill a target.
In this case I think that level 13 Death From Above could be beneficial to a Poison oriented Valeera. If you go unnoticed and the enemies happen to be close together, then you can Stealth into Assassinate on to applying both poisons then a quick Blade Flurry to apply your poisons to all of the enemy heroes in the vicinity.
Speaking of a supportive build for Valeera, level 16's Expose Armor could also do wonders against a beefier target, especially if used in succession with an ability such as Tyrande's Hunter's Mark. It can also be combo'd well into: Assassinate > Double Poison > Blade Flurry > Sinister Strike > Eviscerate. Then if you choose Nightslayer at level 20 you can drop Smoke Bomb and then wait for Stealth to come off of cooldown in order to make a get-away after dealing some additional damage while Smoke Bomb is active.

SIDE NOTE: As I'm typing this a thought just occurred to me: Does Wound Poison also impact Stitches' Devour (his self-heal) ability? The text of the ability says "healing received" and to me that implies from an outside source.

However, I definitely think that Wound Poison shouldn't be taken if they have a hero that offers shielding rather than healing (such as Tassadar or Medivh).

TL;DR: I love Valeera, you can vary her play style so much.

The range reduction on Sinister Strike is sad but usually you can burst down your target faster than they can get away so the damage is well worth it. If you are concerned about not landing Sinister Strike with the range reduction then by all means take Slice and Dice or even Assassinate if the enemy team loves to be split up or you often go to gank a lane with a single enemy Hero.

The poisons are great and I wish there were more of them to be honest. Crippling Poison is my go-to for the AA build and Wound Poison is perfect against a strong burst healer or multiple healers. As to if Crippling Poison can be applied by Blade Flurry to Slow all targets hit, I tested it in Try Mode and found that it is possible, which raises the value of that Talent even more! It even works the same with Wound Poison.

I have yet to try a Blade Flurry (BF) build yet as I am trying to finish my tweaks on the AA and SS builds as well as round out their Build Discussions, but I want to eventually try it to see if Valeera has some high value with it in teamfights.

EDIT: As there is only one Blade Flurry Talent available to Valeera, a Blade Flurry build seems unlikely, however I am going to try a teamfight-oriented build (the TF build) and I have my current Talent choices listed in this guide. Hopefully I can get some good games to continue testing these three builds I have currently listed and other "strange" builds I want to try out.

I completely missed that Seal Fate gives a bonus Combo Point as well as Initiative! If only there was a Talent that let you stock up to 2 additional Combo Points... Anyways, good catch and thanks! I will have to go back through the Talents and decide which one to replace and with what... And I forgot to add the mention of Wound Poison - against multiple Heroes that can heal it is a great tool to make sure you slay your target.

EDIT: Replaced Initiative with Relentless Strikes and added a line about Wound Poison's potential.
EDIT 2: Odd, why was this down-voted?