Semantics gets in the way. Most efficient, least effort most would agree. Finger on the key to depress the key is more economical than raising the finger and striking it. Using weight to depress the key is less economical then using the smaller muscles to depress the key etc. One must assume one is thinking.
Sorry for being such a nerd, but "most efficient" and "least effort" may still not be the best option for musical purposes. A movement that works rather well in slow to medium tempi may fail in faster tempi. A good teacher will know from experience what works best for faster tempi and will have you practise that, even if it is not convenient or easy at all at first. Someone who is on his/her own and always picks the "easiest" options may get nowhere with a virtuoso work.
Also, when one has chord and octave leaps, for example, there are two approaches:
1) press, prepare the next one quickly and press
2) drop, "write" an elipse with the underarm, and drop.
In many works of the great Romantic literature, the second option will often give the best sound results although it is psychologically the most difficult because of the risk involved.