So... ((Effort/Value)-Dependencies)+Time Critical is an equation that will never calculate your priorities. The calculation of priorities requires human interaction, discussion and common sense. Put your stories on a board, group them, talk through the priorities, have your work schedule to hand, move the stories around, discuss the different permutations. What you must remember is that this is agile. Today's priorities are not necessarily tomorrow's priorities. Work with what you know now and adjust as you learn more later.