* A site that is high in the SERPs for your target keywords, but with a low PR
* A page (on topic) with a high PR which doesn't do well SERPs
I gave up linkchasing except via content building and indirect advertising, years ago. It just wasn't interesting and the ROI was poor. That said some considerations:
Unless you are offering oodles of cash there has to be a reason for them to link out to you - often what you have to offer: content, tone, etc. better fits one than another.
A page that is high in the SERPs for your keywords just might consider you a competitor (at least for those terms) so may not be interested.
A page that has high/low SERP in one SE may be the opposite in others - there is more than one SE. Diversity is a good thing.
What are the traffic numbers/sources? Just because a site is high in a particular SERP does not mean that it must get lots more traffic - the other may get tons from blogs or other SM. And would you rather have high traffic low conversion or the other way around - how targeted are the different traffic sources?
TBPR is changed infrequently - do you know their historical positions? Are they likely static or likely to be changing.
What is the rest of each site like? If the high TBPR page is surrounded by low TBPR pages some new internal links could change the situation greatly. And conversely for a low TBPR page surrounded by higher TBPR pages or if it should get (as on topic often does) new backlinks.
And finally - just because TBPR shows high does not mean that it passes any - there are onsite methods of withholding (some can not be easily detected) and what Google passes only Google knows.