Reddit user Rustid has gotten the scales out to test which type of Reese's Peanut Butter candy has the most peanut butter.

Here's the spread of Reese's treats he was measuring:

FYMHOTSAUCE.ROCKS / imgur.com
It included:
Large Reese's Peanut Butter Cups
Reese's Peanut Butter Eggs
Reese's Peanut Butter Hearts
Reese's Pumpkin
Reese's King Size
Reese's Snack Size
Reese's Small Heart
Reese's Miniature
Reese's Mini
Rustid used a scale, ruler, and scalpel to measure the peanut butter – scraping it out of its delicious chocolaty covering.
After everything was measured this is how much peanut butter and chocolate remained:

And these are the final results!

imgur.com
Turns out the Reese's Peanut Butter Heart has the most peanut butter, whilst the small Peanut Butter Heart has the least.