If on 64-bit ARM Cortex-53(Rpi3/Pine64) BSD still lags behind Linux a little bit: FreeBSD CURRENT supports arm64 quite well, but still has some minor issues compared to Linux distros that provide good arm64 ports (Rasbpian or Arch/ARM, don't even waste time trying Fedora or Ubuntu ARM64 ports). OpenBSD 6.2 introduced official arm64 support but is still largely experimental and I wouldn't recommend it.
However, in my experience, unless probably you buy an AMD Opteron ARM workstation, you're not going to see the difference between 32-bit and 64-bit on the 2Gb RAM and the limited A-53 CPU the Rpi3 come with. Personally I've made my tests, and came to the conclusion that on Rpi3, the OS choice is more inportant than a arm64 port. So, my recommendations;
- Void Linux-musl and Alpine only provide 32-bit armv7/armhf ports but eith their feather hardware requirements are the only Linux distros which is worth running as minimal desktop-workstation on rpi3
- NetBSD-CURRENT earmv6hf runs extremely well too on Rpi3, thanks to
ebijun image
- Looking at Forum's threads about Rpi3, FreeBSD (either STABLE-armv7 or CURRENT-aarch64) is another good choice, and there are many here using it, though personally don't,so it wpuld be better to hear their respinse.
Finally, bear in mind that, as far as I know,the only distros fully supporting Rpi3's wireless chip are Raspbian and Arch, while Fedora added it in 27, but after having tested it, I'd say it's still to unreliable. Only sone OSs provide support for Rpi3 bluetooth (NetBSD does for example, and I think FreeBSD too). Anyway, outside the diatro I mentioned above,you'll either need a Ethernet connection or a USB dongle