For my homelab, I used a constellation so I can name each of my server after a star in the constellation. It is on a generic domain extension.
If it is something long term, I’d generally opt for a more stable extension. I.e. vanilla .com/net/org; or cctld for an existing country that you have close ties with that’s not likely to go away anytime soon. It is extremely rare, but this way I’m not running the odd risk of the company behind those fun new extensions, or a country going away (see .yu, no pun intended).