Diana is the easiest of the three, her Q is a very predictable ability and if she misses one you can go in and beat her in a fight, its very easy to dodge because of the arc it has, just remember which way it moves in relation to which way she is firing it, and move away from the arc. With her Q down she cant reset her ult and she loses a lot of her damage. Stopping her snowball is also the easiest if you are playing an AP champ build abyssal scepter the MR + increased magic damage you will deal will help immensely, also warding is very important against her to stop her from roaming and ganking.
Camille is a little harder, but she doesnt play too differently from jax irelia or fiora and stopping her is done in the same way, build a Frozen Heart, it will massively decrease her damage output. Her gap closer is also her CC and she has to use the first part on a wall/ structure first, if you dodge the second part she has no more CC or gap closer in her kit and it has a really long CD. Just like the other 3 champions I mentioned however, she is still very dangerous without it thanks to her ult, save whatever CC you have for after she activates her ult to reduce the amount of time she gets to attack you while in it, as it increases the damage she does. Champions that have the ability to block other peoples abilities (Sivir, Nocturne, and Fiora) can stop her ult from being used on them if timed correctly, putting her ult on CD without it doing anything. Stopping a snowballing Camille can be hard without CC, but that is no different from stopping a snowballing Irelia, but stack armor if you can, her second Q does a lot of true damage, but it has a long CD and has to be timed right to get the true damage off.
Darius is probably the hardest to stop snowballing once he has started but is really no different than Illaoi in that aspect. He has no gapcloser so just stay away from him if he is getting ahead, whoever is ranged on your team should have a pretty easy time of kiting him if they know anything about positioning, also if you are a melee champion fighting him, stay as close to him as you can, his Q only heals him if the blade part of his axe hits you so if you are too close he wont get that healing, it also deals less damage to you when you are in the handle area of his axe.