Valla is currently one of the highest damage heroes in HotS. She has a decently reliable escape and very high right click damage. In addition to her escape (vault), she can escape easily with her passive hatred, which increases her attack damage and movement speed for each attack she has done recently (up to 10 stacks, 2% attack damage and 1% movement speed increase). Her regular abilities are pretty decent, hungering arrow is really good for the early game. Multishot is good for clearing lanes or for slowing enemies down, if you get frost shot at level 13. Vault is your all around escape that moves you a decent distance away, allowing you to escape from a lot of bad situations. Valla is currently really strong because of her ultimate. Strafe is a top-tier ultimate because it allows Valla to do an insane amount of damage while being able to move freely and even vault. Rain of Vengeance is also a decent alternative, if your team has decent control. Though, I highly recommend getting strafe a lot, and becoming comfortable with it.

Level 1

Rancor - This is almost always the go to talent 95% of the time at level one, it allows you a passive which will ramp up your right click attack speed pretty fast, and it will allow you to stack hatred faster.

Cost-Effective Materials - This is probably the only other level 1 talent I get, I only get it if I'm going full arrow build, but as of right now right click build is significantly better.

Level 4

Vampiric Assault - This is probably my go to talent 85% of the time. The lifesteal from this allows you to lane very efficiently early on and I take it almost every time there is no healer and still most of the time when there even is one. It also allows you to solo kill heroes easier since the heal is really strong.

Manticore - This is the talent I almost always take when I don't take vampiric assault. This increases your damage by a decent chunk, but not quite by that much, which is why I take vampiric assault so often.

Puncturing Arrow - This talent is only useful if you go the arrow build, where you can spam arrows and thus get more damage out of them. It also makes arrows easier to land because of the increased range.

Level 7

Battle Momentum - This is also a decent talent, but you may run in to mana issues if you spam all of your abilities off cooldown. However, you won't run into mana issues if you enter a teamfight at full mana. This will also allow you to get strafe off cooldown much faster (although it is already a short enough cooldown, that it doesn't really matter, but it's possible that you may be able to cast it multiple times in a single teamfight if it lasts long enough). I prefer to use this with other talents that boost abilities rather than right click such as frost shot at level 13.

Searing Attacks - This is the talent that really makes Valla shine early in the game; it allows Valla to easily take down heroes that have over extended. It is also very useful in ganking heroes if one of your teammates has a disable. This also has really good synergy with the level 4 talent vampiric assault, in that you will heal yourself for a lot more when this is active, furthering your advantage. I take this 95% of the time.

Repeating Arrow - Again, this talent is purely if you are going the arrow build, which is highly situational.

Level 10

Strafe - I take this talent most of the time, depending on both team compositions. Some players may say rain of vengeance is better because strafe is so easily interrupted. This is true, but you should wait until most interrupts have been used, and in turn use strafe then. This forces the enemy team to either save their interrupts and be weaker in team fights or not save them and get dominated by strafe.

Rain of Vengeance - This can be taken situationally if your team has really good setup for it, and the enemy team has too many reliable interrupts that won't lose them the fight if they save for interrupting your strafe.

Level 13

Giant Killer - This will increase your right click damage by a pretty sizable chunk. I mostly take this on maps where I will not be solo that much, and I take this when the enemy team has some very high health tanks. This is probably the one level where I have the most variance in which talents I actually pick.

Frost Shot - This talent is amazingly good, it is perfect on maps where you will constantly be chasing people down or solo. This is also good for when you take executioner at level 16, since you can activate it yourself.

Level 16

Executioner - I usually take this talent, unless my team has absolutely no reliable disables, or I am in need of being able to burst someone with high health, or have a heal that I can trigger myself.

Tumble - This talent is very situational. It increases your ability to survive by a lot, but you have to give up executioner to take it. So, I usually only take this if I am going the arrow build, so I can refresh the cooldown on arrow with the repeating arrow talent from level 7.

Blood for Blood - I don't go this talent very often, but I can see some use for it in some situations. However, more often than not the heal is not that great for valla, and the damage from it isn't justifiable over executioner. The heal usually falls short, because in most situations you are either bursted down, or you just survive. It is a decent talent however when they have an extremely high health tank, but even then you probably should be targeting someone else first.

Level 20

Vengeance - This just makes your ultimate which was already really good, even better by adding a lot of damage on top of the un-upgraded ultimate.

Bolt of the Storm - This is a situational talent that I would only take if you find yourself needing escapes during teamfights or an additional ability to position yourself in teamfights. Though, most of the time vault will do the trick, so I usually do not take this talent.

Control (RoV)

This is the build I most commonly go in high tier match ups. Some variations are obviously going Strafe at 10 and 20, which I do a decent amount. Searing Arrows at 7 for higher damage output to a single target. Also Manticore at level 4 if I do not need myself to have higher self-healing. Also, Giant Killer at level 13 is a must for teams with multiple high health tanks, and Executioner at level 16.

High Damage

This build is for dealing really high damage and is particularly useful for pubstomping.

Arrow

This build is very situational, and I don't really use it that much anymore. The main idea behind it is to hit many hungering arrows. Don't be afraid to get aggressive with them early, since they do a lot of damage early on if you can isolate them on one target.