The general advice I've been seeing the past ~8 years is "There is no reason to pick Ubuntu over Debian". I don't know who the opposite advice comes from and why anyone would pick ubuntu for a server.
I advocated for Ubuntu for years because it was easier to install and had excellent hardware support. For 2026 I have switched back to Debian because Ubuntu has been making my life more difficult. Ubuntu 26 basically forces you onto Wayland even though it breaks some of my use cases, particularly with screen recording. It turns everything into Snaps which is a hassle because it means I need to mirror both the regular repo and the snaps to my closed network instead of just the repo.
Ubuntu still has the superior installer by a good margin, but it does sometimes like to crash when run offline. Debian's installer at least has the option to go text only. There is also more work to do after the install is finished on Debian, but since that's a script it's not such a big deal.
The one bit of the Debian installer I dislike the most is how if you aren't online when you do the install you get a completely empty sources.list, and the Debian sources are a lot more complicated than Ubuntu's. Debian's support for third party drivers like nVidia graphics is also more complicated and confusing than Ubuntu's.
I deployed Ubuntu on a LOT of servers 10 years ago because at the time, they had a track record of doing good things in, with, and for, the Linux and open source community. I had already been using it on the desktop for a long time by that point and knew it well. Ubuntu was far and away the most popular; it was a very safe and sane choice.
That changed when they started heavily promoting Snaps as the next big thing and started putting features and updates behind their enterprise offerings. Basically, they stopped being "Debian, but better." And Debian also made lots of incremental improvements in user-friendliness in that time. Basically, Debian is now pretty much what Ubuntu always promised to be.
Enterprises love paying for support contracts. If you have one, you can demonstrate something has been accounted for. A secure software without support is worse from an audit perspective than a security disaster with proper paperwork. Most of these people never actually involve support they paid for ever.
The only recent reason I’ve managed to come up with is it far and away has the best support for Nvidia’s various drivers and utilities for running GPUs and its assorted ecosystem, like Infiniband and Spectrum-X Ethernet.
If there’s another option I’m unaware of, I’d love to hear it. Also to be fair, I didn’t evaluate Sid for this, only Stable.
Platform support. Oracle Cloud for example only provides images[1] for Oracle Linux, RHEL, Ubuntu, and Windows Server. Anything else you have to bring your own.
[1] https://docs.oracle.com/en-us/iaas/Content/Compute/Reference...
I've set up a new server literally couple weeks ago on a droplet on Digital Ocean - Ubuntu LTS is the default choice(you can select other distros but Ubuntu is the default). So I guess I picked Ubuntu because I haven't done Linux admin in over a decade and it's presented as the default choice by a big cloud provider.
15-20 years ago the joke was that Ubuntu is a Zulu word that, roughly translated, means "I don't know how to configure Debian". Ubuntu was one of the first distros that allowed one to easily download proprietary WLAN drivers without dealing with the terminal, ndiswrapper, or compiling half-broken OSS implementations; for this reason it caught fire with those who wanted to try Linux but were otherwise unwilling to engage in such shenanigans. I tried it on a laptop around this time and was quite impressed. This reputation for "it just works" has carried them ever since even though other distros now do largely the same thing ( cheap, obscure, or recently-released hardware excepted).
I took the lazy Mint route with my most recent machine since I wanted to use it for light gaming with minimal fuss. I'm going to redo it with Nix sometime soon because the value prop simply isn't there and I'd like to try a declaratively-configured distro.