Salt/Puppet/whatever. I ignore them all. Why? I have put a lot of thought in to this area.

IMHO, the overwhelming problem with salt/cfengine/puppet style solutions (which I will refer to as 'post-facto configuration tinkerers', or PFCT's) is that they potentially accrue vast amounts of undocumented/invisible state, therefore creating what I refer to as configuration drift.

IMHO, a cleaner solution is to deploy configuration changes from scratch, by deploying clean-slate instances with those changes made. In addition, versioning one's environment in this way creates an identifiable point against which to execute automated tests. (This class of solution I refer to as 'Clean-slate, Identifiable Environments' or CSIES.) Examples are Amazon AMI's, and any other kind of versioned/identified VMs.

PFCT's deployment paradigm tends to be relative slow and error prone. CSIE's tend to be fast and atomic. PFCTs are headed for the dustbin of history. They are temporary hacks that clearly grew from old-school sysadmins' will to script. CSIEs embrace modern day devops, as more holistic entities that embrace virtualization and recognize the integrity of the environment as critical to preventing ridiculous numbers of environment-induced, service-level issues that are an expensive tangent to service development, testing and deployment. Thus, I would argue that what we are looking at with PFCT's is a failed paradigm, and with CSIEs, the now real and current opportunity for something far more elegant.

(Disclaimer: Haven't tried ansible or vagrant first hand, but they do seem to be PFCT's to me.)