This is a huge question, but it seems to be positioned as either/or.
DevOps is just about bringing ops, programming, and test together, mostly through automation.
Agile is about collaboration, small chunks of work, valuing done work over done documentation, etc.
I see the two as compatible.
DevOps allows you to release more often and with less risk. Agile implores you to release more often but doesn't tell you how.
So you could say that DevOps enables Agile.
So do 'em both!