The discussion of Emblematic Units from recent decades brings up an interesting broader point: because, since the introduction of the atomic bomb, major powers haven't fought each other, it's very hard to make judgments about the merits of weapons, because they've only been employed against opponents tactically inferior by orders of magnitude, usually in a context of absolute air control. Taking the A-10 as the example, perhaps if NATO had fought the Warsaw Pact in its prime, it would have emerged that the AH-64 always did better because it could hover, or perhaps the helicopters would all have been massacred by man-portable missiles and the A-10 and aircraft like it would have been the only game in town if dedicated ground attack craft were desired. It's just impossible to say. This is why, while I mentioned possible alternatives, I don't really have a preference among them and my position on the US Emblematic Unit is basically "anything but the F-35."
Because of the ongoing discussion, I just Googled the A-10 and, according to Wikipedia, the plane is still in service and plans have been made for possible extension to 2040.
https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunderbolt_II