Should I choose a postdoc with greater potential for collaboration over a higher ranked institution?
I would suggest going where you think you'll be happiest and do the most productive and visible research, taking into account whatever factors of these places are relevant to you.    Ultimately your chances at a faculty position will depend on the strength of your results and on your letters.  

The advantages of going to a more prestigious place is that, in general, such places have a higher concentration of good mentors and collaborators.  Such factors make it easier for most people to get good results and high visibility.  But in your specific field, for your specific needs, a lower ranked department might be the better fit.

If you were saying you were considering department #100 over #5 (via some standard ranking), I might suggest you consider such a choice very carefully.  However, a "30s" department might easily be a better choice than a "top 15".