I had a site for a small while and I offered a trial. I think 80% of the people who signed up for the trial cancelled right after signing up.
And I had a lot of content too, for a very small price, but they just went inpo cancelled right away, and downloaded everything.

Today, if I was just promoting it myself I wouldnt offer a trial, Id just offer the monthly membership.

If you have affiliates then I think you have to offer a trial because the affiliates want to see there making some kind of money, even if its just a few bucks.