My vote is Archlinux. Debian is sometimes a little too "optimisitic" when backporting security fixes and upgrading from oldstable to stable always comes with manual intervention.
Release-based distros tend to be deployed and left to fend on their own for years - when it is finally time to upgrade it is often a large manual migration process depending on the deployed software. A rolling release does not have those issues, you just keep upgrading continuously.
Archlinux performs excellent as a lightweight server distro. Kernel updates do not affect VM hardware the same they do your laptop, so no issues with that. Same for drivers. It just, works.
Bonus: it is extremely easy to build and maintain your own packages, so administration of many instances with customized software is very convenient.
Not because of Arch itself and its quality, but because you need to constantly monitor the mailing list for issues and you need to plan a lot more downtimes due to reboot. This is not gonna happen in businesses.