I have started using chef to automate build environments on top of vagrant. One thing that made me choose chef is windows support: chef uses winrm on windows, + things like powershell, and that seems to work better than puppet (e.g. I could not for the life of god make a unattended install of visual studio with puppet).

On the - sides, I don't find it particularly well documented (it feels like reading the MSDN, where things are self-referentials), and it is quite slow.