Pinap Berry

Nearly always on Magikarp.

Usually on Eevee unless really high cp.

Often on low cp Pidgey. Not so much anymore though.

No other commons.

On any other mon I'm currently trying to get candy for, unless high cp or known to break out/flee.

On rares that I really want candy for, only if low cp. If I see a wild Blissey/Snorlax/Dragonite/Tyranitar with high cp, there's no way in hell that I am using a pinap.

Anything rare like Vulpix and Growlithe (don't have double fire yet), especially when farming nests, but not on starters unless they're very low level.

Always on Magicarp, Dratini, Rhyhorn. Usually on low CP Eevees.
If I have more than 20, I use them on any low CP.
(1000 item bag)

On mons I need candies for.

I use them on virtually every Dratini. I think mathematically the lost ones are far outweighed in terms of candy by all of the caught ones in the long run. I also use them on lower CP Snorlaxes and stuff like that.

Mostly I use them on Pidgeys and other 12 candy evos. This keeps my bag from becoming too full while allowing me to work to my next XP egg run much more quickly.

I use it on larvitar, dratini, dragonair, dragonite, mareep, snorlax, lapras, starters, exeggcute, chansey, blissey etc.

Dratini, dragonair, dragonite, Latvitar, mareep, snorlax, lapras, Machop, chansey, Abra, Kadabr, Houndour,
If I have more than 20 berries then will use it on Magikarp, chinchou, starters, exeggcute, eevee,

Magikarp, Rhyhorn, cyndaquil, Charmander, houndour, phanpy, snubbull, Grimer. Basically low cp mons I don't come across too often.