In nonstandard humorous terms the difference between goodest and gooder
is that goodest is superlative of good while gooder is nominalization of good.
As a noun gooder is
nominalization of good.
goodest
English
Adjective
(head)
(nonstandard, humorous) (good)
Usage notes
The standard superlative is (best) gooder
English
Adjective
(head)
(nonstandard, humorous) (good)
Usage notes
The correct comparative is (better)
See also
* do-gooder
Noun
(
en noun)
(nonstandard, humorous) nominalization of good
Usage notes
New England slang, as in: "You're a gooder, for taking care of your mom."
A parallel construction to oner, a nominalization of one, to mean "an outstanding person or thing."[http://www.thefreedictionary.com/oner]