You could either start with the free version and then upgrade when necessary while working on your return, or you could find your specific forms on the chart at the link below and make a decision up-front based off of the information you have received.
https://turbotax.intuit.com/personal-taxes/online/deluxe.jsp
If you scroll down a little on this screen and click the "Tax Forms" tab, you will be able to see a side-by-side comparison of each version for each form/schedule. You can also sort this list and search for specific form names.