Generally speaking, BAK-4 prisms, large objective lens diameter and large exit pupil
Decades ago, as an ocean-going sailor I was choosing marine binoculars with compass. In the store I compared Steiner, Fujinon, Bushnell and a highly respected marine supplier store brand, side by side in extended evaluations at a store in a marine setting. I was surprised that the visible benefit to me was not easy to discern, the most expensive was not clearly better (but subtle) than the lesser-priced binoculars all at the top of the line from each manufacturer; the bargain binoculars had non-optical compromises, and those are best evaluated in the hands of the specific buyer, not unlike driving a car is subjective to each driver.
7x50 vs 10x50...7x gathers light in low light better, 10x gives more detail, but with a more shakey image that gathers low light less well. Smaller objective diameter simply gathers low light less well., at the benefit of lighter weight better portability. you decide your preferences and pick your poison.