Page Rank vs TF/AF when it comes to your Web 2.0 root domain

I have gathered a list of a bunch of Web 2.0 sites that allow you to create websites/blogs. With PR becoming less and less important, should I focus on the PR of the root domain or the TF/AF more? I would think TF/AF, but does PR have any importance anymore?

For example, I would have mywebsite.wix.com and I would be checking the TF/AF & PR of wix.com... that's how it would work.. right?

Is their any advantage to using a whole blog and posting to your site with one post over just making a post on someone else's blog (Guest post)? I'm guessing that there should be a good ratio to look natural right?

I've got lots of questions, haha

Use the TF/CF for checking the quality of web 2.0 sites.