On my "old" '19 1.5L I just upgraded from the stock mount (polyutherane one) to 2.0T casted mount, did exactly want I wanted, didnt even mess with the lower. Now that I have my 2.0T 10 spd immediately went for hasport (70A). I however run stage 2 and maybe soon stage 3 phearable, and put my coilovers back on with sway bar so everything is going stiff. I have the upper in, waiting until next oil change to put my car on my lift and change lower mount. only a few hundred miles and already way less vibration, but not bad, feels great to me, can hear the engine way more in the cabin. All about what you perosonally want/can tolerate.
From and engineering perspective, there is something to be said about changing one and not the other, by you sitffening a "beam" (engine) on one side and not so much on the other making there a possiblilty of causing premature wear on the new mount. It is stiffer than the stock mount so the stiffer mount now will take more of the "weight" from engine/engine movement, reducing its life sooner than the same two more stiff mounts. There is also something to be said about the fact that there is a third mount of the transmission- possibly 4? and I am unsure if they even make upgraded transmission mounts yet or at all for the accord. Stiffening the engine mounts can lead to vulnerability of the other mounts. Unsure if changing any of them indepent of the other causes any premature wear on itself or other mounts since they are not all the same stiffness.
I plan on changing both, but I would be curious to see if someone changed only one if the new mount wore out faster becuase of the uneven stiffness.Probably would have to see 50k+ miles before you could really see.