My picks were as follows:
Performance - It’s useless in two of three pillars, and while it has some function in the social pillar, it’s far less directly useful for getting NPCs to do what you want them to than the other Charisma skills. Most of the time, it just ends up being “roll to see how much you impressed an audience” skill, which tend to be pretty low-stakes rolls
Medicine - No real use other than stabilizing dying characters, which is done more reliably and more effectively by any source of healing. Might also sometimes be used to gather forensic clues in a murder mystery type scenario, but those uses are often brushed over, given that failure on them can cause the players to get stuck. Not pure flavor like Performance, but extremely limited usefulness.
Acrobatics - Almost everything you want to use Acrobatics for is actually a function of Athletics. As-written, Acrobatics is really only used for maintaining balance, which… I mean, how often does that even come up? Not much in my experience. Beats out the previous two because at least you can use it to escape grapples and restraints if you have low Strength/Athletics.
Nature - by far the most useful skill on this list, as it, like all intelligence-based skills, is often used for information-gathering rolls. Ends up being the lowest-ranking int skill for me, only because it often overlaps with the more generally useful Survival skill.
(Dis-)Honorable mention to Sleight of Hand, which under the 2014 rules I might actually rank below Performance, since it’s also mainly a flavor pick, but instead of being used to impress an audience, it can only really be used to get pocket change in a game where money is useless, at the risk of getting yourself and maybe your allies into trouble if you fail. In 2024, it shoots way up the list due to now being the assumed “pick locks” skill.