SSD upgrade or more RAM, which single upgrade actually gives the best real world speed boost for an ageing PC

[ObserverEffect68]

When an older computer starts to feel sluggish, the two most commonly recommended fixes are almost always the same, upgrade to a solid state drive if the machine is still running on an old mechanical hard drive, or add more RAM if the system frequently feels like it is struggling under multiple open programs at once. Both upgrades are relatively affordable and reasonably easy for most people to do themselves compared to a full replacement, but they solve genuinely different kinds of slowdown.

An SSD dramatically improves how fast the operating system boots and how quickly programs actually open, which tends to be the upgrade most people notice immediately in everyday use, while additional RAM mainly helps when a system is trying to juggle too many things simultaneously and starts relying heavily on much slower virtual memory as a workaround. For someone with an ageing machine and only budget for one upgrade, which one do you think actually delivers the bigger real world improvement?