Ogryn
5-8% Strength for 4.5s on Kill. Stacks 5 times.
5-8% toughness on Chained Hit.
Your Grenades stick to Ogryns and Monstrosities. 6-15% Damage vs Ogryns and Monstrosities
Melee horde: Push attack > HA > LA > HA > LA
Crusher trains and monsters: Ability + Rumbler and/or Throw grenade box
When you kill enemies in melee, you get a chance to free fire the rumbler. Just weave it in when you feel like it.
4 points left over. You can grab Batter in the middle for bleeding melee. Bruiser for more ability up time. Massacre+Lucky Streak for better dps. Lynchpin+Steady Grip for better toughness gen. Your choice of damage resistance in the middle of the tree.