I've used both Blogger and Wordpress which are great platforms. Currently I'm using B2Evolution for no other reason than I've not used it before. I really like it though mainly because it is just like blogger in that if I want to create a seperate blog I can with just a few clicks of a button. The only draw back is that you do have to have some experience with html and such to get the most out of it and they don't have nearly as many cool plugins as WordPress.