For me Valla's "Hungering Arrow" & "Arsenal" are strong enough off the hop, I like this build because it gives you overwhelming power in your basic attacks. I find that very useful combined with "Strafe" for its ability to spread out large amounts of dmg too multiple heroes and minions at once. Along with "Stoneskin" for a little extra survivability, surviving things like Nova's "Triple Tap" if timed correctly. Level 20 "Nexus Frenzy" is always fun, taking your already badass build to another level! My Valla is almost Level 12, I recommend this build! Good luck and have fun!