You are comparing apples and oranges. The combination of PR and pa isn't really going to help you as much as some other Moz metrics. If you are spending time and effort getting links as opposed to mass spam stuff you will want to focus on the subdomain mozrank of the potential link your are getting. Especially if it is a blog related link. That is because your page will grow in authority over time as google indexes more pages on that website that contain links back to that specific post. Great links grow in value over time and crappy links dont. Domain authority is valuable, but it can misrepresent the value of a link if the following occurs:
The website uses spammy methods to link build (Linkscape doesn't do a very good job of determining the difference between contextual based links and comment spam.
The link you are getting is on a subdomain of the website (DA takes into account the domain mozrank which is different than the subdomain which is more important. Especially on hosted blogs like wordpress, blogger, or typepad)
I have asked Ran, and tend to agree with him that you are much better focusing on links on high authority subdomain mozranks with low PA than low domain authorities with a high PA.
That being said. Make sure you also take into account the amount of links on the page. Whatever authority you are going to grab is going to be split amongst those links. It may also be beneficial to spend a proportional amount of time evaluating to the value of the links. If you have a choice between two websites that are in the 70's of DA range you should be spending a lot more time evaluating than DA's in the 20's and 30's