Disqus (The system we use on BNR blogs) seems like the easiest and best choice. The only compelling arugment I can think of for going a different route is if we were looking for a truly free option or if we wanted to silo ourselves from the BNR blog for some reason (Even then, we could just make a new account).
- Already used on BNR blogs so might promote cross traffic (There's a link in the Disqus form to see all conversations across BNR)
- Free if we can piggy back off the existing plan
- Otherwise $10 < 50,000 daily views