Moving the same thing (your body) from the same starting point to the same end point will accomplish the exact same amount of work, and therefore require the same amount of effective energy to accomplish, so it boils down to biomechanical efficiency of which movement more efficiently accomplishes work, and wastes less energy.

That’s going to depend on the individual, as everyone’s limb length and muscles and tendons will affect how efficiently the body maintains forward momentum once in motion, how much energy is wasted on each step, etc., so that the ideal step size is different from person to person, and the ideal speed is different from person to person. The answer will change for the same person with training, too, as the biomechanics of a particular movement tend to get more efficient when that movement is trained over time.

You may be able to estimate the right answer by just doing it both ways and seeing what a smartwatch tells you. The gold standard would be to hook you up to a machine that measures your oxygen consumption, but that wouldn’t be very practical.