The first build(Smash) shown is very versatile, you should try to consider other talent options by looking at your team, enemy teams and map.

The second build(Soul sucker) is viable if you want to cut out "especially tankers" real fast. His percentage damages will quickly drain any tankers life effortlessly. It is also useful if you want to slow enemies who are trying to run away. If you have assassins who are specialized to lock in and kill a target you should try to provide them vision when you are dead. Also your slow will make them hard to escape once your teammate locks in.

Try to land both Q and W on the same target to maximize the benefit.

If you think that a big fight is going to start, use your E to close the gap between enemy assassins, you will easily kill them or at least scare them away so they can't participate in the fight.