Energy use increases with bpm, change in pressure (systolic - diastolic) and the stroke volume (amount of blood pumped per beat).
Note that there is also an inverse relationship between stroke volume and bpm because the faster the heart beats, the less time for blood to return to the heart for the next beat.
That said, heart “strength” is more about reserve capacity (ie ability to ramp up when necessary) than energy efficiency. It’s like comparing a Ferrari to a Corolla: at 100 mph the former can still increase its power whereas the latter is getting near its limit.
So if the Ferrari has a “car attack” and suddenly loses 50% of its max speed then it can still keep up on the highway, the Corolla maybe not. That’s more important than which one is more energy efficient.