What should I brew: a breakdown of the costs and gains of brewing 

Here's some data to help you choose which potion is best to brew. 
Overall, brewing Antidote to Common Poisons gives the greatest points reward per hour, while Herbicide, Sleeping Draught and Swelling Solution are the cheapest potions to brew (per potion) as all their ingredients regenerate. Don't forget that you have limited galleons, so spend wisely. 

Ultimately the choice is up to you, so have a look and decide which suits you best :)

   

Pewter Cauldron

Potion	Points gained per hour	Points gained per potion
Antidote to Common Poisons	10.5	7.0
Cure for Boils	4.0	3.0
Forgetfulness Potion	9.0	9.0
Herbicide	9.0	9.0
Sleeping Draught	9.4	11.0
Swelling Solution	7.0	7.0
Wideye Potion	9.8	9.0

Brass Cauldron

Potion	Points gained per hour	Points gained per potion
Antidote to Common Poisons	12.4	7.0
Cure for Boils	4.7	3.0
Forgetfulness Potion	10.6	9.0
Herbicide	10.6	9.0
Sleeping Draught	11.2	11.0
Swelling Solution	8.2	7.0
Wideye Potion	11.7	9.0

Copper Cauldron

Potion	Points gained per hour	Points gained per potion
Antidote to Common Poisons	14.0	7.0
Cure for Boils	5.5	3.0
Forgetfulness Potion	12.0	9.0
Herbicide	12.0	9.0
Sleeping Draught	12.7	11.0
Swelling Solution	9.3	7.0
Wideye Potion	13.1	9.0

Overall cost per potion

Potion	Cost (galleons) per potion
Antidote to Common Poisons	0.38
Cure for Boils	0.33
Forgetfulness Potion	0.50
Herbicide	0
Sleeping Draught	0
Swelling Solution	0
Wideye Potion	0.33

Note: Cost per potion is calculated by the cost of one ingredient multiplied by how many are consumed per potion

The prices, locations and uses for ingredients can be found here.
The locations of regenerating ingredients can be found here. 

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(Data and images provided by WolfsbaneDust164 and MidnightMoon126)