IBT is on the stronger/darker side, Darjeeling is on the lighter side.
IBT should be rich, dark, high in caffeine, with a strong flavor that doesnt get overpowered by milk, or ruined by a little oversteeping. It can still be burned if you use water that's too hot.
Darjeeling should be amber-colored, light tasting, moderate in caffeine, and should have some floral notes. The flavors can be drowned out by milk or oversteeping in my opinion. Best black and lightly steeped in sub-boiling water.