I can see 30 day trials getting you a higher conversion rate (greater value), but 14 days to payment rather than 30 is good.
Which should you use? I can see a standard answer being "split test it and find out," but for many companies that assumes a certain amount of traffic. For small operations just starting out, what factors can help make an informed decision in the absence of data (i.e. not instead of, but until they get enough traffic to test)?