It would have been fair to say it aged well, if the version which is currently called testing was their flagship version.
For most software, the testing version gives you relatively latest stuff. But that doesn't mean every software can advertise itself as being up-to-date.
For debian specifically, I don't think they recommend using the testing version unless you're a Debian contributor/tester.
I've tried using Sid (desktop) in the past, but ran into several version issues while installing through apt. Didn't try much to debug, and switched to stable. Been a happy user since!
In my experience 'sid' is what you typically use on desktops, 'testing' on servers you actively maintain, and 'stable' for servers that you just want to keep running without much fuss. 'sid' can have some interim issues, but nothing significant enough that it would disqualify it from desktop use; and 'testing' is really solid already for those who don't feel like power users much.
For most software, the testing version gives you relatively latest stuff. But that doesn't mean every software can advertise itself as being up-to-date.
For debian specifically, I don't think they recommend using the testing version unless you're a Debian contributor/tester.
I've tried using Sid (desktop) in the past, but ran into several version issues while installing through apt. Didn't try much to debug, and switched to stable. Been a happy user since!