For what? Are you building an embedded system, are you going to run it on a server, are you making a firewall, are you going to use it for software development (and if yes, what machines will your software be deployed on), or are you just using it as a desktop? To answer the question whether FreeBSD is appropriate, or whether other BSD operating systems might be more appropriate, we need to know what your goals are.
... because of: the lack of systemd ...
Why? What has systemd done to you? Has it created any problems for you? Has it made development difficult for you?
Here's my story: I use both Linux (several different flavors), MacOS, and FreeBSD. I develop software, including daemons (programs that get started at boot and run at all times) on both FreeBSD and Linux. And while I don't enjoy using systemd (the configuration style is strange, the integration of zillions of functions into one package is undesirable, it has too many prerequisites which makes creating a small installation impossible), I actually like creating daemons that run under systemd, because systemd takes over a lot of the work that daemons usually need to implement, and does it for them (in a more reliable fashion).
I'm not saying that Lennart is a good person or a fine software engineer, nor that systemd is well engineered. All I'm saying is that for a user and developer, it can actually be pretty good.
I suspect that you want to get away from systemd either based on politics (for example the common GPL hate), or because of second-hand information.
... and I was interested in the HAMMER2 filesystem (I know that this is DragonFlyBDS).
Many people already said that ZFS's features are mostly a superset of Hammer.
What is the use of your file system? Long-term archival storage, desktop, serving other machines, in particular SMB/CIFS clients (typ. Windows and Mac)? How big is your file system, and how many disks do you intend to use? What is your plan for durability and availability (RAID, redundancy, backup)? This affects what file system to choose. My personal answer: Use ZFS whenever possible.
I don't know which distribution to choose:
Others have already commented, but let me try to make this clear. Linux has "distributions". That's because the only thing actually called "Linux" is a kernel, which is trademarked by Linus, and distributed in raw form by kernel.org. You can actually download and compile just the kernel and use it (embedded developers sometimes do that). But for normal users of operating systems, you need other stuff, for example utility command such as ls and rm, integration with daemons such as cron and getty (without getty, nobody will ever log into the machine!), setting up the networking infrastructure (such as setting the IP address of a network port), adding compilers and linkers (such as gcc or clang), and sometimes adding an X-windows based GUI (such as gnome or KDE). This packaging is what is called a "distribution". Typically, the large distributions (such as RedHat, SUSE and Debian) also modify the kernel (very few or none actually work well with an unmodified kernel.org kernel).
On the other hand, the various BSDs are not distributions. Instead, they are complete operating systems, including separately developed kernels and userland, and different packaging with contributed software (called "ports" or "packages") such as the GUI. They separated from each other about 15-25 years ago (the three big ones, NetBSD, OpenBSD and FreeBSD all got started in the early 90s, DragonFlyBSD in the early 00s). And for each of them, the "base operating system" (the kernel and the basic utilities) are not packaged together, but actually developed and designed. So for example the FreeBSD version of ls (while mostly identical in the source code with the NetBSD and OpenBSD versions) will have changes that are done by FreeBSD developers for integration of the rest of FreeBSD.
To a large extent, the largest difference between the various *BSD operating systems and Linux distributions is this: Any one BSD system is actually coherently designed, and things like project goals, release cycles, portability, man page style, documentation, and quality control are consistent, across the whole OS. This does not so much extend to packages (and the DE/GUI is typically a package), which are typically only minimally patched for each BSD. To the consumer of an OS, this leads to a different "feel": Similar to MacOS, using BSD makes you feel like you are dealing with a unified and consistent body. On the other hand, in Linux you often notice that different components (such as Apache, Bind, and baseutils) have different styles and different mindsets.
