They both achieve the same thing in different ways, but it comes down to philosophy if that even matters to the user. You can build gentoo for example with openrc or systemd, and depending on what you do you’ll need to integrate things differently (using elogind with openrc since logind is systemd specific). In gentoo it affects how you’ll compile. Its really a non issue, but it all depends on what level folks wanna spend on something that could potentially be different. I use openrc daily on multiple setups and it took maybe a week of using it to get the hang of it. Its just operationally different.

Does it really matter for most folks? No. But if its something you find interesting, it can be a nice change based on personal views and principles. I run openrc because I personally as a programmer don’t believe in how “proprietary” systemd is designed, nor agree with the decisions the maintainers have made. That’s just my opinion. At the end of the day it doesn’t technically matter.

This is a more hardcore viewpoint but it covers a lot of the issues folks have with it. https://suckless.org/sucks/systemd/