Which gear ratio is ideal? deciding gear ratio

[mickztlin]

so we plan to buy 3 CIM ball shifters from west coast products, but the problem was unlike the dog cim shifters (which are more expensive) they don't have the gear ratio to speed chart under this project. If you are reading this you are probably thinking "why don't you look at the options of ratios and decide based on that?" Sadly, I don't understand how to pick the proper gear ratio and I would like to know for the future. So to clarify, I would like to know which gear ratio to pick, and how to understand what i am selecting. Sorry about the noobish question, I am more of an electronics person. Thanks for the responses!