Re: Is WPMU preferred over WP for BP?
…I want all member blogs on a single site…
If you want to offer your members their own blog, then you will need to use WPMU. The fact that each of your members has their own blog does not mean they have their own site. All the blogs are located on and served from your site.
If you only want to have one blog but offer a social networking layer on top of that using BuddyPress, then single-version (solo-blog) WordPress is all that you need. But, with both WPMU and WP, BuddyPress will allow you to create a social network. As Andy says, the only difference is whether you want to offer your members the option to create their own blogs on your site.