Without knowing anything about your product or service, my gut instinct would be the 7-day free trial would work the best. With that in mind though, what works

Without knowing anything about your product or service, my gut instinct would be the 7-day free trial would work the best. With that in mind though, what works for one person with one product/service may not always work for the next so my A/B results (I don't have any for this type of test) would vary to yours most likely. The results are going to also vary based on the overall presentation of your site. To me personally it is trivial to set up an A/B test with available tools that the best route, and to get the most accurate results, to go is to conduct your own A/B testing using your product/service and your own site. This is especially critical with the timespan question you ask as well.