The frenchified formation"more correct" is preferred, but the native English formation "correcter" is not incorrect. It does have lower status, though, and is considered unsuitable for writing. School-marms will keep "correcting" it until you become an accomplished author and then it will be a robust element of your style.
The comparative degree for "lush" is "lusher."
better for its comparative and best for its superlative
The comparative degree of "muddy" is "muddier".
The comparative degree of the adverb "sadly" is "more sadly."
Shier (alternate spelling shyer).
More correct
Neither. Pretty is the positive degree. The comparative is prettier; the superlative is prettiest.
The comparative degree of "holy" is "holier."
Teapot is a noun and, as such, does not have a comparative degree.
The comparative degree is wider.
"Less" is the comparative degree of little.
More wicked Most wicked
Thriftier is the comparative degree of thrifty.
The comparative degree for "lush" is "lusher."
The comparative degree of "light" is "lighter."
better for its comparative and best for its superlative
"Speed" is a noun and a verb and, as such, does not have a comparative degree. The comparative of the adjective speedy is speedier.