Im 5'7 and 135lb. My first board was a 151 based on internet calculator and the fact it was the size of the $70 craigslist board I happened to find. Now I ride 149cm. Big boards are clumsy, no?
If it's your first board, it doesn't really matter. If you plan on keeping it for a long time (ie. no money to upgrade), I think you should go smaller.