Which is more preferable: lowering the gaze upon seeing 'awrahs, or not returning a greeting of "peace"?

If women are young and unveiled, and there is a fear of fitna (temptation/strife) from returning their greeting, then it is prohibited to return the greeting in this situation. There is no contravention of Sharia in not returning the greeting. It is obligatory not to look at them, or initiate a greeting, or return it, in order to protect oneself from the forbidden.