@mjg59 When it comes to the kind of software that has multiple implementations, I've found the best way to pick a winner is to check the license.

The implementations that are (totally or mostly) under pushover terms almost always suck (i.e. BIND).

But when I find one that proudly states that it is under the GPLv3-or-later (for example, KnotDNS), I know I've found the winner right away.