We have a set amount of money that we can spend each month on Press Releases and buzz and we can either have 1 PR 8 website that is fairly relevant to our site or 3 PR 7 websites that are relevant do the review. Which would be more valuable in terms of link power. I'm not really sure what the difference in direct traffic we would get but I was curious of the PR 8 with a high rep is way better than three PR 7 links.. ( I'm trying to not make this based on PR but that is the one variable that I'm not sure about ). :)

Which choice is likely to send more direct traffic?

I agree, press releases arn't going to help with SEO too much, traffic is the reason for press releases although I do see alot of other SEO's using them for links, not something i would personally bother with, they are like forum links (not static) and have little if any real SEO benefit. If you are looking for a good one to drive traffic to your site I would recommend www.prweb.com a couple of hundered dollars can get you quite a bit of homepage exposure and alot of traffic.

If the entire monthly marketing budget is to be spent on just those links, I'd say don't. Doing a press release is a one time expense, and beyond that there are still plenty of directories around worth being listed in, though it takes a bit of hunting to find them.