What I would choose with your setup, will not be only one secondary OS, but just a couple of partitions with different system setups:
2.AmigaOS 3.1 (ClassicWB P96) - Some eye candy and plenty of handy programs
3.AmigaOS 3.1 BetterWB - For enhanced performance (it is speedy)
4.AmigaOS 3.9 + BoingBags - For having the latest OS and its built-in packs
5.Aros 68k - just pick a stable cdrom image (not ArosVision, because it is not designed for real amigas)
6. AmigaSYS 4 - Like Amikit but less bloated and designed for real hardware.
I find Amikit is really cool for WinUAE and, Amikit Real is great for AGA amigas with a 68040 and plenty of ram. But I wouldnt choose it for your current machine configuration.
Linux 68k is pretty outdated, I wouldnt touch it. The same goes with OpenBSD. Stick to NetBSD which is currently being mantained and Amiga support is well cared for.