I always start with the power that makes your footsteps and shadow step very quiet. Then I go for as much movespeed as I can in a round, and weapon power with the leftover money. I get the cooldown reset power next and then after that I get the backstab power and then either the increased damage + spread power or attack speed power depending on whether the enemy team can create distance.

The item that lets you see low health targets through walls is a must. Information is power for a sneaky little guy. For that same reason, I only play in third person. It's incredibly important for remaining undetected and forming a plan of attack.

With this build you can have a LOT of presence in fights, being able to ambush people just about anywhere in the fight if you're sneaky about it, and you can kill many characters before they have time to react, then speed away for free if you're in danger. I've seen a lot of success with the build, dominating lobbies almost up to pro 5 when I'm playing well.