driftdown speed
In practical application, the driftdown speed will give you the slowest rate of descent if you lose an engine at altitude. In swept wing jets, it's min drag speed. (...and of course this varies with weight.) It will keep you higher longer while you formulate a plan.
I disagree that it will give you the most air miles. Min drag will give you the most "time" before flameout, but best optimum range (specific range) speed will yield the most NAM per unit of fuel. That speed is significantly faster than min drag.