brain is once again busy with the question: NSD or knot?

This is neither urgent nor hugely important.
Both are plausible implementations of the usual stuff i like to see and use, with mostly minor differences.
And migration should be entirely possible — which serious authoritative server won't support plain zonefiles, catalog zones, TSIG, primary + secondary modes, … aka. "the usual stuff"?!
(Yeah … i've seen software failing to properly support TSIG :dragnangry:)

But somehow this brain likes to get stuck on advantages of architectural decisions, the control interface specifics, available metrics, … ^^"

The even funnier part: i'm in a position where i could reasonable manage my zones manually as handcrafted zonefiles, including serial. :neofox_floof_angel:
(This obviously quickly falls apart with other folks' zones, but wellp … even there most would likely be primarily interested in adding a few more secondaries, which is trivial either way.)