Linux

Gentoo, for its user choice and lack of bloat. I've been using it for a long time, and can create my own packages for personal use if I don't mind them looking like Frankenstein bodges, so that's another plus. It's stable enough if you stick with actual stable-marked packages and don't go out of your way to shoot yourself in the foot, and if something does go wrong at the distro's end, 1. they usually fix it pretty fast and 2. rolling packages back is easy if the older version is still in the tree (and usually still possible if it isn't, although it can get kind of involved).

Would I recommend Gentoo to another user? That depends on which user. You kind of have to be either knowledgeable or willing to learn—it isn't a "just works" distro, although some things have been streamlined in recent years. You do have to put a little time into maintenance, but it's usually on the order of less than half an hour a week.