for the lvl 13 talent you can pick Frost shot if they have no tanks. but even then i still prefer giant killer.
A lot of people like to pick Rain of vengeance ult but i find Strafe a lot better when you pair it up with searing attacks, its good for mowing down people trying to get away, just vault in click searing attacks and strafe. as for the lvl 16 attack i have seen a few people pick Executioner but i find blood for blood much better, it can turn the tide of any fight, they chase you thinking they got you, you click that and all of a sudden you have more heath then they do and from there its an easy kill. the lvl 20 skill i know Bolt of storm is said to be best, but i like to dish out the max amount of damage i can, i am kind of a suicidal player i go in and almost always take out 2 or 3 people before dieing and let my team take care of the rest.