How to decide the membership model?

Free vs Paid? If it is free; -give it away totally for free and try to make money from ads or -give it away for a limited time/limited extension and force them to be paid or leave If it is paid, how to adjust pricing? - make the entry level very low so that we can gain as many members as we can and then try to make the current ones higher paid members. or - adjust member levels accordingly so that there is no easy entrance but when they become member they will worth something All ideas are appreciated. Thanks.