Debian stable is an obvious choice for projects that don't rely on too much "new stuff" because we already have a lot of stuff that uses APT, deb repositories, etc. Otherwise, probably CentOS/RHEL for those situations that are just ultra-averse to incremental change and prefer a HUGE change once every 5-10 years.
I think we might become a bit more adventurous and move to e.g. NixOS for "newer" projects. That's probably going to have to be trialed for a few projects before we go all in on it, but it seems really nice for servers (and dev machines for that matter), but it'll be interesting to see if you have to truly go all in to reap the benefits. (The worry here would be the amount of upstream 'support' in terms of manpower to bring in security updates, etc.).
(I'm also vaguely aware of SuSE, but I only spent a very brief period of time with it about 10-15 years ago and don't really remember any distinctive features either way. Which is kinda weird, because it seems to be known as the 'popular in Europe' distro?)
