Check with your sponsors. Webbilling offers sponsors the ability to offer free and paid trials on direct debit non-card joins for Germany, Austria, Netherlands, Spain and the United Kingdom - if you are sending this country-traffic to sponsors only accepting credit cards you are losing money...they need Webbilling.com to capture every join...
To the question - I am seeing more sponsors opting for low paid trials recurring in 3-30 days than free trials...