Valla is one of the best assassins in Heroes of the Storm.She can easily escape and in the same time her burst is insane.
For the first tier is better to pick Composite Arrows.Why this?Well that is your main spell for team fights or killing fast.
For the second tier Arsenal is really good for more damage.
For the third tier the only thing that is useful is Searing Attacks.There's no need to comment here.
Fourth tier Strafe is good not only for team fights, but for killing them while you run away.You can use Vault while ulting.
Fifth tier here you can take what ever you prefer.For me Frost Shot is good for chasing anyone.If the enemy team has more than 1 tank then you should pick Giant Killer.
Sixth tier Blood for Blood is a need.This talent saves not only you, but your whole team.Staying alive is very important if you want to win the game for sure.
Seventh here you can choose again what ever you prefer.For me Nexus Frenzy is the best.You are much harder to reach and with the bonus attack speed if he gets near you, he ll be dead in no time.
Hope you like it, leave comments if something is wrong.Piece