I've unlocked a dragon cookie in Cookie Clicker. What's the best aura to use at each stage of game play?
A lot of this will depend on which auras you have available, and whether or not you are actively clicking the golden/wrath cookies that appear.
If you've gotten them all and unlocked the second aura from sacrificing 200 of each building, and are actively clicking cookies, then using Dragonflight and Radiant Appetite can provide a lot of cookies.
If you are letting the game go, then Radiant Appetite and Breath of Milk will provide a lot of cookie production.
If you only have one aura slot (have not sacrificed 200 of each building), then Dragonflight when actively playing, and Radiant appetite when you are not would probably be most effective. If you have not yet gotten Radiant Appetite, then Breath of Milk will probably be your best bet.
Note you can always switch and aura if you decide to play passively or actively, but it will cost you one of the most expensive building you have purchased.
Finally, if you are about to ascend, it could be worth switching an aura to Earth Shatterer, and sell all your buildings for the extra cookies, especially if you have the chocolate egg waiting to be upgraded from the Easter season.
Here are some reddit posts of people discussing this topic:
In early game, I think before you get the Radiant Appetite, the best aura for idling is Elder Battalion, not the Breath of Milk. Elder Battalion gives way more CPS when you don't have all kitten upgrades. I don't know the point when milk becomes more powerful than battalion though.. I assume after purchasing the Kitten managers.. (900 quintillion)
In mid-game I recommend to play little more actively. Because when you get Dragonflight, you can then start "hunting" the Frenzy AND Dragoflight combination. This can give enormous boost even if you're clicking manually. (Using macro or automatic clicker could give INSANE amount of cookies). If idling, you should use Breath of Milk.
In late game when you have all auras, all kitten upgrades (and possibly second slot for aura). Try to get that Frenzy+Dragonflight combination when playing actively and Radiant Appetite for the second aura. If idling, use Radiant Appetite and Breath of Milk and let wrinklers come.