Neither are that hard, FreeBSD has the additional challenge of overcoming Linuxisms. Just takes a little reading, and the FreeBSD Handbook is an excellent work.

FreeBSD has been a learning curve for me in terms of learning kernel development and things like kqueue and ZFS. I didn't find it difficult in terms of getting started, since it is a lot like Arch in terms of setting up things like X windows.

FreeBSD is actually a much cleaner operating system than other unix-like clones. I have used it for a decade but my work required me to use linux.

Best parts already mentioned in this thread (pf, jails, etc.) I would add one thing to the list:

https://www.freebsd.org/cgi/man.cgi?hier(7)