I kind of reject that there's an ideal because while there is a average lip/chin length and range that most people without jaw or facial issues fall into yet it still is not remotely absolute or important in overall attractiveness. Of course significant deviations will causes aesthetics to decline.
However like you demonstrated there's so much variation, you get good looking george clooney with the looooong upper lip and chin. You get the short upper lip and chin Tom Hardy with super full lips AND deep mental labial fold with recessed profile (yet a class I bite).
I think lip:chin ratio is not like other traits relationally e.g. the excessively short or long middle third of people's faces (think David Schwimmer) or excessively close set or wide eyes... which are pretty much unalterable and have a huge impact even if the rest of your face is "ideal".
EDIT: To answer your question, I think the balanced thirds is more important because you see plenty of "short" lip people who show tons of upper teeth yet are good looking without jaw issues. But you know what, maybe I'm wrong! haha
EDIT2: Ok forget to say there are values tossed around, usually 1:2 ratio, upper lip to lower lip (which most superior point of lower lip to bottom of face so entire chin). I've also seen 1:2.2 ratio.
I just measured mine. It's almost exactly 1:2 ratio, s**t it's close. But I've had double jaw surgery and my lower third was already close to normalish I think pre-surgery.