You use whichever ultimate suits the battle, i personally like the blast furnace cause in late game i can easy take away over half of an opponents health (all of it if its a low health assasin). Victuals is good cause then you rarely need to go to a fountain or base. If the enemy team has a character that often or always is stealthed you should pick invogoration instead of chop meat, but be weary of the mana.

You should use this if they have alot of here that has alot of escapes, if they have alot of assasins and low health heroes they will have alot of dmg so use the brand with alot of care (preferably on the highest health hero with litle escape), use the lamb of the slaughter here.