This build is the perfect balance of auto attack, hungering arrow, crowd control, and survival.

This build is excellent for overall DPS vs. heroes, as well as chasing a weak hero down with vault/puncturing arrow combo.
Blood for blood is excellent when used against a target with a large health pool especially at high levels because it will almost always bring Valla back to full HP.
Rancor, Giant Killer, and Nexus Frenzy are great for high DPS auto attacks, and I have easily reached over 100k hero damage in matches as a result.
Valla is still capable of clearing the occasional wave if needed due to Multishot with the Repeating Arrow combo. A few auto attacks with two Hungering Arrows and a Multishot volley can destroy even siege units.
Lastly, rain of vengeance is what really earns Valla the title of assassin. It's stunning ability coupled with high damage can wittle down even tanks, followed by other cooldowns to ensure Valla finishes them off.

Overall this high DPS build puts Valla into tier 1 status with a combination of auto attacks, stuns and chase down blows.