Escalate from force to violence only as needed
Start with a threaded separator tool if you have one. (And if you don’t, save up and get one; they’re great for saving joints that are still usable.) If that doesn’t work, the sledgehammer or air hammer on the knuckle is the next-least-destructive way. If that doesn’t get it, well… it’s game on, because that joint probably isn’t making it out alive.
Pickle fork (or pickle fork on the air hammer) follows, with the understanding that the joint boot is probably shot and the ball joint will need replacing, then pickle fork with sledge, then torch.
Hopefully that helps a few of you who haven’t been doing this for years and years. A surprising amount of tools are needed to remove ball joints, but once you’ve got ‘em (and a little know-how on how to best use them), they’ll pay for themselves many times over.