This depends on whether or not you intend to expand your website into something that will be invested in for many years to come. Permanence and reputation are the hallmarks of those who intend to be working on the web for a lifetime. We have found that there are very few problems with journaling under a common blog domain like blogger.com We seem to rank fairly well inside of most large important search engines even though we do not own more than one of our domain addresses. This is good given the condition of our pocket books.
However, one word of caution to ministries that intend to sell merchandise. It is far better to own your own domain name under these conditions simply because most Christian search engines are biased against listing blogs without individual domain registrations. It would be better for a large ministry to own their own software or rent it from a reliable company and then attach a blog to it. Or link to a free blog from a visible tab inside of their web pages. In this way, you will not be "turned away at the door" so to speak, when your web master goes to list you under multiple Christian search engines. We do not understand this biased behavior on the part of Christian search engines but we do know that it is a very real problem.
