Hello,
Oracle actively supports two VirtualBox release lines: 5.0 and 5.1. In my experience, 5.1.x releases are a little faster in some operations, but have some annoying bugs that 5.0.x don't. Oracle prominently features 5.1 as the default download, and it is also the version in the repos of most Linux distros (Debian Jessie backports[1], Testing and Unstable, Arch, OpenSUSE, OpenMandriva, Ubuntu 16.10 - only Ubuntu 16.04 LTS has 5.0).
The CI test for our Vagrant images already tested with libvirt-kvm and VirtualBox 5.0; I extended it for testing with VirtualBox 5.1 as well, in a branch, but the test fails because sclo-vagrant1, based on upstream Vagrant 1.8.1, only supports VirtualBox up to version 5.0 (support for 5.1 first came in Vagrant 1.8.5). Are there any plans to upgrade sclo-vagrant1 to a more recent upstream version, or perhaps backport the support for 5.1 to the current sclo-vagrant1? [2]
If you'd rather update to a newer version, Vagrant 1.9.1 broke at least private networking (eth0 is preconfigured by our image, but the additional network interfaces that Vagrant 1.9.1 configures don't get an IP address - I assume public networking is broken as well, but I only tried private networking). I also saw some entries concerning NFS in the upstream issue tracker, not sure if it's caused by the same bug. Versions 1.9.0 and 1.8.6 work for me.
Best regards, Laurențiu
[1] https://www.debian.org/security/2016/dsa-3699 [2] https://github.com/mitchellh/vagrant/commit/b57b0e0d48fe8b4196ca6b7e01bb6c1e...