Favorite Lightsaber Crystal?

There are a few that I find really cool so it'd be hard to name one but here are the main ones:

Lava crystal: It's a much more weighted blade, which already takes away one of the criticisms I've had about lightsabers which is their lack of inertia. And it drips lava...which is epic. Downside of course is it has more danger to the user even requiring gloves to use it, but still, epic.

Tainted Nightsister crystal: Probably mostly cause I love night sisters so much, but it creates a choking putrid green mist and a green blade, which I find just fascinating. As most lightsabers don't have any effects beyond enhancing focus/use of the force and the actual cutting ability of the blade or minor changes.

Ghostfire crystal: Mostly I find this cool just due to it's assassination purposes, as well as how in theory an opponent couldn't tell when the blade is on or off, which makes the use of acting as if it is activated, but only turning it on after they try and defend themselves, ever so much more interesting.

There's another I heard about which had a freezing effect of some kind which I also find fascinating in it's application but I don't know where that went.