Have you come across the Jankó keyboard? https://en.wikipedia.org/wiki/Jank%C3%B3_keyboard
The last question implies some kind of absolute value system, not just your own personal taste (even if you're the one making the ranking).
However, I would argue that it also loses some impact. It removes the idea of a person having to decide what "best" or "worst" actually means. Instead, you would need a follow-up question of "why?" to clarify that particular point.
For instance, I would have answered French horn. That instrument can single-handedly cut through an entire orchestra, and there is no mistaking it when you hear it. The harpsichord would be a close runner-up. So I'm probably looking for unique sounds that are easy to pick out of a crowd.
The best instrument is the one I like to play the most, duh. Yeah, "that's just my opinion, man". Which was kinda the point.
I don't know what else to tell you. You ask "what the obsession with ranking" was, I gave you the answer straight from the article. Is it "best" for you? Probably not. Again, duh, that's not what the answer said.
It said so right in the article: you learn what you care about. Best musical instrument? Easy, mandolin. Maybe the violin. Both are tuned in fifths, so scale and chord patterns are transferable up and down, and across the fretboard/fingerboard. Far better than that bastardized tuning of the guitar. Play a melody, play rhythm (on the mandolin) if you have to, though not as good a choice as a guitar. And don't get me started on all the keys of a piano.
But that's what I care about in a musical instrument, mainly because I play one. YMMV, and it likely will if you don't play anything.