If there is any performance difference between those two it probably isn't much. I've used both that you mentioned and several others, they all are quite similar.
I've been using Armbian for the last year or so. Armbian has a gui based utility where you can choose where the OS is installed. On my NanoPC-T4 I have the boot files on the eMMC and ROOTFS on the M.2 nvme drive. It is stable and very quick.
I know you have problems with your camera and the USB3 on the NanoPC, I do as well.....the Armbian 5.xxx mainline kernels fix the problem but they are newer and need work. Wifi doesn't work among other things, but my ASI294 MC pro works great on the USB3.0 port.
Kstars is qt so a kde desktop is best. Plus atm kde has very low memory use and is very quick. Kde neon works great, latest stable kde and uses Ubuntu as its backend