PRWeb vs. Free Press Release Sites

[Ruby707]

Greetings,
I understand that issuing press releases with linked keywords and whatnot can be good for SEO, and I actually have some newsworthy content coming up, so my question to the forum: Do I need to go through a paid service like PRWeb to maximize the SEO AND news value of my releases, or would I be just as well off going through the free PR distribution services?

I've got a half dozen reasonably newsworthy announcements coming in the next few months, so I want to make sure I'm getting the biggest bang for the buck on all of them. But of course, I don't want to spend any money doing it!