Let's go Straight to the point and explain why this build is the most effective:

Tier 1
+As you are an assassin meant to do heavy damage, Rancor is the only ability that grants more DPS than other ones, also, it will make synergy with: Hot Pursuit, Vampiric Assault and Giant Killer
-Punishment just help you get stacks quickly, but your auto attack can reach the top 10 by itself in few secs
-Composite arrows can already hit all minions in a lane at early game
-Low mana cost on arrow and helth regen is not enough to make a powerful build

Tier 2
+As assassins tend to be very fragile, this talent help you to keep attacking and even take merc camps alone. Consider to take this one even having a healer in your team as you will increase your time attacking in 1v1 hero fight or clearing lanes
+Manticore is a good talent too as it can do synergy with giant killer for heavy damage, but you will pay the price to die fast if there's no healer in your team and you won't have enough Regen to sustain a 1v1 fight
-Puncturing can be helpful to increase your range, and as it prioritizes heroes, you may be able to kill heroes trying to escape, however, for that matter is better the talent in next tier
-Arsenal also can be a good choice to clear lanes and push, but as you are an assassin, that won't be of enough help in team fights

Tier 3
+Hot pursuit gets the advantage here as it helps you as attack-defense: you can chase and kill heroes easily, but also have more speed to scape if getting surprised + your dash
-Caltrops are almost useless as when you usually try to escape is for prevent being ganked, so other heroes can easily avoid the fall in caltrops unless they are very close to you, and in that case you are most likely dead
-Repeating Arrow is an overall choise as it helps you to do continuous damage or take camps faster, however, is hard to sustain mana to keep using your abilities, an you may find yourself with no mana when trying to escape or use heroic
-Searing Attacks are also heavy damage, but again it can be tricky because as your attack speed is high, you might find yourself with low mana when trying to escape or use other abilities

Tier 4
+Strafe is a good choice for team fights that also suits to beginners, as it does damage to enemy heroes around you, you don't need to worry about aiming or other thing than to stay close to other heroes. However, if other team has high stun (Muradin + Uther) this heroic is reduced in duration and damage. So remember to keep your distance and always keep moving
-Rain of vengeance is also a powerful option but has the inconvenience of being a small line attack that has to be aimed properly, hence, if you fail first wave, second is useless, but also after first wave, second one may be avoided, so damage may be reduced to 1-2 heroes only in the first wave

Tier 5
+No question here, giant killer is the best choice to increase your overall damage and be a real threat to other heroes in team fights r 1v1. Also does synergy with vampiric assault to sustain your attack before trying to escape
-Spell shield is rather for tanks that have to be in front line absorbing other team's damage
-Tempered by discipline would be a good option if it were in the second tier instead of vampiric assault, as it ensures up to 30% regen, but at this moment of the battle, you need to increase your attack rather than healing, which is fair enough with vampiric assault
-Frost shot only helps to slow down enemies with 0 increase on damage, which is the most important thing on an assassin. If this were in Tier 3, it could be a good option instead of hot pursuit, as this one ensures quick slow to both, finish heroes or escape from heroes

Tier 6
+Blood for Blood is the best option as it will not also do damage, but return the double as healing, so it can be used when at mid health against a tank so your team can finish him and the rest of the team
-Stoneskin has only half of the benefit of blood for blood, though the shield is increased, you need to also focus in damage as an assassin
-Tumble sounds like a 100% escape as it can be cast twice, but again, this has no advantage on damage and both vaults consume mana that can be used on your arrows or multishots
-Executioner is also half of the benefit of blood for blood, as id does more damage but only for heroes with some anomaly, which may be for very few time without the benefit of 20% healing

Tier 7
Lot of choices here, but best one is nexus frenzy, as you have increased attack speed that stacks with your rancor and synergies with giant killer and vampiric assault. As you also have more range, you can now attack from more distance and improve your escape escape
-Bolt of the storm can be also a good choice, as this really ensures to escape from death. However, i prefer to increase damage with attack speed as we have covered escape with hot pursuit + vault
-Storm of vengeance has the same problem that if first wave don't hit, other ones are useless and avoidable as Kael's Fenix. Could be a good option if the wave width were increased
-Vengeance sounds like a good option to take, however, i prefer to gain permanent attack speed and range increase as it synergies with giant killer and vampiric assault