I personally think AROS ( AROS Research Operating Syste ) is pretty cool. Same with just the basic Amiga Workbench 3 series ( the only one I have any experience with ).
Obviously Amiga Workbench isn't daily driver ready, but neither is AROS since it's, from what I can tell, just an Amiga OS passion project trying to make a more modern more open source Amiga OS.
My favorite is Debian, with systemd uninstalled. At this point, you can't install Debian without systemd, but you can uninstall systemd after OS installation.
It used to be that most desktop environments in Debian depended on libpam-systemd, which depended on systemd and systemd-sysv. More recently, desktop environments just depend on libpam-elogind and elogind which is only part of systemd, and allows you to use sysvinit.
I prefer sysvinit mainly because I find it easier to create custom services out of my own programs. My success rate at doing this in systemd is 1/3, and in sysvinit about 10/10.
I also had a problem where a Debian-based embedded system had some kind of broken NTP client running on startup, and due to systemd, I couldn't figure out how to disable it. It would set the time to several years into the future, as soon as it first got a network connection on each startup.
I have no moral or philosophical objections to the design of Windows NT, just the company that makes it and the enshittification. If ReactOS ever becomes stable enough to be daily used I would use it. For now I use LinuxMint and Steam OS at home.
Since you asked for OS and not Linux: OpenBSD and FreeBSD are beautiful systems w/o systemd. I would switch in a heartbeat if I wouldn't need Linux for work reasons.
Neither Haiku or 9front use systemd, and they're both very interesting from a technical and design perspective (though not for their init systems).
If it has to be a Linux distribution I would say Damn Small Linux (DSL), because its really impressive just how few resources it requires. You can run x windows and even browse the web (using Dillo) on a system that's small enough to fit in the L3 cache of some modern CPUs.
I don't daily drive any of these though, so they might not count as my "favorite".
I have to say as someone who uses NixOS I love systemd, because it makes a lot of things very easy. For example hardening services ( systemd-analyze security) or replacing cron (system timer).
systemd is fine. The only people I've ever heard complain about it are lonely neckbeards pretending like their opinion somehow matters.
I've used Debian as a server system since it was using init.d. And do you know what I found? systemd is easier. And the fact that Debian of all distros decided to use it says a lot.
So the old init.d system was better? Come on people, let's stop infighting. I have zero preference on init systems. You know why? Because they're just plumbing. Stop this nonsense. Do I click on an init system? Do I use the init system to check my email? Or play games? No. I know poettering can be controversial, but let's just move on. Run freebsd if you're so butt hurt.
System service managers like systemd, OpenRC, runit, or SysVinit often come down to user preference. While these systems are crucial for initializing and managing services on servers, where uptime, resource allocation, and specific daemon behaviors are important, their impact on a typical desktop or laptop is generally minimal.
For most personal devices, the primary functions of a service manager occur largely out of sight. As long as the system boots reliably and applications run smoothly, the underlying service manager rarely registers as a significant factor in the daily user experience.
For many, including myself, systemd simply works without much fuss. My choice to stick with it isn't due to strong conviction or deep technical analysis, but rather the simple fact that I've rarely, if ever, had to interact with it directly. For my personal desktop and laptop, it reliably handles booting, service management, and shutdown in the background. If it's not broken and isn't hindering my daily computing, there's no compelling reason to explore alternatives.
As a user, why should I care whether the distro I use uses systemd? I use Mint and I don't remember having to interact with that kind of low-level nonsense. The distro maintainers can use whatever reasoning they want to pick these details.
Alpine Linux would be my favourite, although I only use it as a server distro. I use Artix as my daily driver for personal computers because of the AUR and glibc (Alpine is musl). I also enjoy Void but it's not got as much software as Artix repos + AUR.
Debian, installed without systemd as per the wiki. So far I've not hit any issues, whilst I've recently ended up diving through both kernel and systemd code to find the root cause of an issue I was hitting on one server. I could have just bodged past it, but I wanted to actually understand what the issue was, and what else it was going to affect.
There are few system manager (single project or a mix of components) that use linux features efficiently and none have dev resource remotely comparable to systemd. That's why in practice systemd is the best system layer implementation on gnu/linux. Android and chromeos userland (upstart derived) are not exactly (freedesktop) gnu/linux.
EDIT: the post ask which OS though. Including userland I like android a lot, but I would say illumos distros (OI currently). illumos has a system management similar to systemd (contracts in place of cgroups for example). Actually systemd was heavily inspired by SMF too.
postmarketOS, though they are in the process of migrating to systemd. Not that I personally mind terribly much, even if it feels like a bit of an odd choice. So maybe I should say Alpine.
Artix has the most amount of alternative init systems available.
I would recommend Devuan, but it just wraps SysV in runit as a service manager rather than just using runit as init.
Gentoo has options for systemd or openrc. You can get runit or s6 to work on it if you're pretty familiar with how /sbin/init works,or so I've ascertained from researching, but have not done this yet.
Void is very interesting as it uses runit and also uses musl instead of glibc. I don't think it has quite as many packages as Artix though due to lack of AUR, and I can only estimate that the use of musl instead of glibc necessitates the need for some interesting workarounds from time to time.
I use Artix with runit. Have been daily driving this for around 6 years now and have been very happy with it.
If I were to use anything else I'd go through the trouble of installing Gentoo and configure it to use s6 init. Just to get more granular control.