I am pretty sure anything => pr 3 is a good link exchange to have, but what about pages with pr 1,2 etc..? How many of these would you need to increase your rank substantially? Thank you
Neither. You should just focus on building quality backlinks and improving your site with new fresh content. PR is just a number, nothing more!
The higher the PR... the better. So if you can get a PR3 then it is lot better than PR1 or PR2. One PR3 is equivalent to almost 101 PR1.