My favorite is sublimation because its one that you can see happening and its a bit surreal.. Camphor is an easy and fun one as you can extract it pretty easily with some basic setup, or just buy it (they sell it as a superstitious thing to certain groups so oddly you can find it at the right stores). To see a solid object just slowly (or if you heat it up quickly) disappear into nothingness is always cool to see as it doesnt seem real.
A very close second for me though is supercritical point, especially if your lucky enough to see it (its usually at too high a pressure to see but there are youtube videos of people creating high pressure clear chambers to witness it). Like sublimation its one of the few phase changes that you can watch and its surreal and cool to see, though sadly unlike sublimation you are unlikely to be able to witness it or experiment with it yourself without investing a decent amount of money.

Other types are really cool but there is nothing to actually see, to it, so its not really as fun even if its pretty cool.. Those would be

1) super conductivity, but especially type II (not the type you normally hear about) as that gives rise to the flux pinning effect

2) Quantum condensation is also a cool phase state change as it allows light to be slowed down to super slow speeds and other cool effects.

@freemo@qoto.org My brain is too smooth

@freemo Great poll!