I bought my macbook 2006 1,1 used and i want to reinstall the OS so everything from previous owner is whiped clean? Which OS is best for these older macs? There are a few to choose from and i want to know which 1 will keep my older mac running the fastest

I bought my macbook 2006 1,1 model used and i want to reinstall the OperatingSystem so as to completely remove all remnant files from the previous owner but the previous owner did not include the startup/OS disk. I was wondering which of these operating systems available( snow leopard, lion, mountainlion) is better for these older macs. Right now i am running OSX 10.6.8. I dont need the best one overall i just neeed the one that will keep my older macbook running the fastest. Im leaning towards snow leopard but probably just because thats the cheapest but i really have no idea which Operating System runs best on these older macs. Any responses will be greatly appreciated. Thanks for your time guys.....