I mean, if the goal is "install a niche kernel for the sake of it", sure that's... a reason, but all the modern non-mainstream kernels (aka not Darwin or NT) at least have a purpose as to why you'd pick them.
* Linux is the de facto kernel used on most servers, has great support and is the third pick after the mainstream kernels for a good reason. It's also usually someone's first introduction to Unix-based systems these days, so there's loads and loads of documentation available (even if the quality of that documentation runs the gamut from "acceptable" to "who wrote this").
* BSDs are rock solid and a great pick if you're targeting reliability. Knowledge on a BSD changes little with the years and that's a big bonus.
* Plan9 is interesting because it provides a unique approach to system design by taking the "everything is a file" approach to its logical limit. That doesn't make the system itself the most useful in the world but it is an excellent system to study and borrow good ideas from.
The main reasons I can see to use Hurd are... ideological opposition to Linux and being a microkernel. While the latter has interesting implications, the usual GNU problem of "we don't try to support any hardware unless it ideologically conforms" really gets in the way of wanting to use it and that's definitely a broader GNU problem but it's a much larger for problem for something as crucial as a kernel.
Also not helping things is that to my understanding, Hurd kind of has a start-stop nature to its development - that is, the project is on life support unless someone starts dissing it, so it picks up back for a few months to show how it's totally alive. Very much more of a spite driven project these days than a legitimate option.