Inshadowsidream

What do you do when you can't decide how to start a story? I can't decide on whether to start with a trip down memory lane, revealing what brought the protagonist to where he is in life, or to get on with it, letting his history be told in bits and piecs in later chapters. Either way would work, but I cannot decide which way to go. I was hoping for some advice in urging this nag out of the gate.