The Butcher is a very good Assassin hero in Heroes of the Storm. Depending on your build he has some mana problems early on, and his mobility can be an issue if you're more accustomed to characters who can quickly and easily escape a bad situation. He also suffers from longer cooldowns than you might expect, but if you have a god team surrounding The Butcher, he can be a devastating DPS. Even with bad team chemistry, if you know how to get around some of The Butcher's weaknesses, he is one of the strongest DPS heroes in the game.
Hamstring is great because it slows enemies for two seconds and The Butcher's next basic attack will strike immediately after a Hamstring for additional damage. It's a fairly straightforward attack and should be used if an enemy attempts to flee from The Butcher. This ability is good whenever it's available, but it's especially useful to make it harder for opponents to escape The Butcher's grasp.
This is The Butcher's primary healing ability. It doesn't inflict as much damage as Hamstring, but when it's used, all of The Butcher's basic attacks will heal him for 75 percent of the damage for the next five seconds. It's a good idea to follow this with Hamstring so that your next basic attack strikes immediately, but either way it works well to help replenish lost health, especially as the game progresses and The Butcher's basic attacks inflict more damage (and thus heal for more). The healing is doubled against enemy heroes.
Ruthless Onslaught is The Butcher's most damaging basic ability. The Butcher charges at his target, becoming Unstoppable in the process, and stuns them for one second if he reaches his target. Depending on your distance from the target, this can't really be used as a reactionary stun, although it can work if you anticipate Jug of 1,000 Cups from Li Li or something similar. This should be used primarily to chase down an opponent and stop them from getting away, while still inflicting considerable damage.
Whenever an opposing minion of hero is killed near The Butcher, they drop meat. As The Butcher collects the meat his attack increases my one percent per stack. However, all stacks are dropped if The Butcher dies, and it will take some time to get back up to his maximum damage potential. This is another DPS class that can become a death machine if they go long enough without dying.
Level 1 - Victuals or Invigoration
Level 4 - Envenom or Cheap Shot
Level 7 - Abattoir
Level 10 - Lamb to the Slaughter or Furnace Blast
Level 13 - Crave Flesh or Burning Rage
Level 16 - Blood Frenzy
Level 20 - Nexus Blades
At level one you have a choice to make based on your team composition. If you have ample support on your squad then you should opt for Invigoration, which causes Hamstring to cost half the mana and have a cooldown of one second less if it hits an opposing hero. If your support isn't great, go for Victuals to heal for three percent of your maximum health every time you collect meat.
When you reach level four your choice should almost always be Envenom to add a poison element to increase your damage output. You can also go for Cheap Shot, which causes Hamstring to inflict double the damage to an enemy that has been slowed, rooted or stunned. Look at your team composition to see how often this could happen before you opt for Cheap Shot. While The Butcher can stun, then use Hamstring, it's far more effective if other members of your team are setting you up for a Cheap Shot.
There's really no question about your selection at level seven. You should almost always be going for Abattoir in order to maintain maximum damage output. With this ability The Butcher can stock up to 35 stacks of meat, and only loses half of them when he dies. The Butcher is an Assassin class and damage is his main purpose, so this ability is a given at level seven.
Once you can select a Heroic ability you have another decision to make. If you have good team chemistry and your team will be stunning enemies left and right to setup attacks, opt for Furnace Blast. This area of effect (AoE) attack can cause severe damage to a group of enemies, but it's far more effective if another teammate pins them down first. If you don't have anyone on your team who can do that, Lamb to the Slaughter is the better option as it pins down one opposing hero for four seconds, dealing damage and allowing you to finish them off with relative ease.
At level 13 your choice should depend on how the match has played up thus far. If you've been able to get in close and stay there until you finish off an enemy, go for Burning Rage. It causes The Butcher to inflict moderate damage to any enemies close to him. However, if you've had to really stick and move to make sure you don't get focused to death, you should probably opt for Crave Flesh. With this ability, anytime you connect with Butcher's Brand, you gain a 30 percent increase to movement speed. This can help you chase down an enemy, or give The Butcher a much-needed escape option.
Your level 16 ability is a no-brainer. Pick up Blood Frenzy to increase your attack speed by one percent per meat stack. With Abattoir selected at level seven, your maximum meat stacks increase to 35, which means that you can increase your attack speed by up to 35 percent. That's a huge increase and causes The Butcher to become nearly unstoppable. The longer you stay alive, the more difficult it becomes to stop this killing machine.
Finally at level 20 you should opt for Nexus Blades so your basic attacks inflict 20 percent more damage and slow your target for one second. If you're looking for a DPS build this should really be your only option at this level. While some people may want o pick up Bolt of the Storm for an escape option in case you get into trouble, it's a little late for that kind of ability at level 20, and if you've been having issues with that, you're probably not playing The Butcher well in the first place.