The Killing Curse is definitely the worst. I mean, really, it's killing someone! Now, punishments. I guess for some circumstances, the punishment doesn't really fit. Like, as some others have mentioned, if used in self-defense it's slightly more acceptable. Just my two cents.

I feel that the Cruciatus Curse (Crucio) is the worse curse because it causes a pain like no other, while Imperius Curse (Imperio) and Killing Curse (Avada Kedavra), you can't really feel that they are in use.
The punishment is the same, a life sentence in Azkaban.
Is that fair?
This isn't fair because, it depends how you were using the curse if you were using it for the sake of using or using it to take over the world. But if you use it as a self defense like Harry did against Bellatrix (OoP) he used it without thinking!
A Dementor's kiss.
Is it a punishment at all?
Yes a Dementors kiss leaves you souless and yet you still live, but on the other hand, you won't know your souless so your not really suffering!

A lot of people have stated that an Unforgivable is okay to use in self defence? But surely it would be better to simply use another curse, such as a disarming spell, if you're in such a position. No punishment and you're not lowering yourself to the opponents standards. Either way, to use an unforgivable, you have to really mean it and a lot of those who are casting one purely out of self defence, probably wouldn't be able to make work.

Therefore, perhaps having the same punishment for each is agreeable?

I don't like the dementors kiss, a life time in Azkaban is really enough for anybody to have to endure. I agree with what others have stated and how no one, not even the Minister, should have so much power as to decide whether a persons soul should be sucked out of their body. But there are ways around using an Unforgivable, whether you are in such a position to use one or not.

It's hard to really decide on one curse being the worst. As they are all horrendous.

The physical torture and pain of the Cruciatus curse that they have to endure is awful, and can often leave people with long lasting illness. Neville's parents, being a prime example of this. Although we have no other examples of such things occurring, there could very well be.

The imperious curse, really depends on how it is being used.
If the person who has cast it, is making you do something such as murder your family, or something equally as disturbing. Then it would probably over rule the Cruciatus in that respect, because you are going to have to live with the grief of what you have done. But naturally, if what they forced you to do isn't all that bad, then the curse itself wouldn't be as bad.

The Killing Curse is painless. But has nasty effects on friends and relatives. It probably has the most long-term effects.

It really is hard to say which curse would be the worse.

The Unforgivable Curses are: Cruciatus Curse (Crucio), Imperius Curse (Imperio), Killing Curse (Avada Kedavra).

Which one of those curses is worse?

The punishment is the same, a life sentence in Azkaban.

Is that fair?

A Dementor's kiss.

Is it a punishment at all?

To me the cruciatus curse is the worst of all, as it can be used all the time on a victim, look what it did to Neville's mum and dad, it made them mentally ill. At least with the killing curse it's all over in a split second and the Imperius curse is mind control which does not necessrily involve pain.

In crimes of this nature (in the fantasy wordls or real world) there is no real punishment for such evil crimes.

I think that all the cureses are just as bad as eachother. i mean the are all unfergiveable so i think that the punishment that you recieve when you use a curse it fair.

i think that all the unforgivable curses deserve placement in Azkaban because they are all unforgivable and there cant not be different punishments depending on the curse used.

It depends really. If you use them in self-defence I don't think that you deserve a life sentence in Azkaban. Every curse is horrible in her own way. The imperius curse can be used in many different ways. Like when Barty Crouch Jr. demonstrated in Defence Against the Dark Arts class. He made the spider jump around, but he could've just as easily make it drown. The cruciatus curse causes extreme pain, but if it isn't inflicted for too long, it won't leave any permanent damage. But if it is, it will result in mental injury. Avada Kedavra does kill, but the victims feel no pain. The worst case scenario would be using all three. Imperius, cruciatus and then Avada Kedavra.

Unforgivable curses are good when good people use them in good ways for example for killing bad wizards and witches and also for tourtue to make them telling true and maybe only the imperiuos curse isn`t useful. My favorite is CRUCIO, and it has the most powerful name.

Unforgivable curses are never good, or they wouldn't be called unforgivable. But honestly, if I was in a duel with someone who used them I'd probably use them too.

I agree with you...