Thanks for your answer Lisa. I also read your blog article "The Next Myspace" and found it very insightful.
I think that if I want to commit really to making money online I'll go for SBI. However for now I have much more excitment and fun doing this community website. I'll just do it in order to learn and know that it will probably have a little audience and be mainly for me and my friends. With that in mind I'll definitely go for Joomla! and MyBlog as it is much cheaper.
But maybe in a few months, if I'm still enjoying so much the website creation world, I'll go for a money making site with SBI!
I think this forum is great by the way