Arthas is probably the most flexible hero in the game right now for talent choices. While the deathcoil talents at 4 & 7 tend to be the better choices you can still flex for biting cold at 4 and icebound fortitude at 7 if you need the dmg boost and dmg mitigation. Level 1 is typically at your own discretion and I advise you to take eternal hunger as a last choice. 13 & 16 are just like 4 & 7 for talents. The AOE upgrades are typically the best, but you can definitely consider the W upgrade at 13 for more consistent lockdown on the enemy heroes and obviously the embrace death talent synergizes rather well with the deathcoil upgrades at 4 & 7. Lastly for storm talents the only one that I consider not worth taking is the army of the undead upgrade. The upgrade for syndragosa is quite powerful against enemy disengage comps and anti-magic shell is just perfect for mage and AP heavy teams. Death's advance is good if you want good engage, but have army of the undead for your ult as it gives you the bonus move speed to try and catch the enemy running.