Quickest.
quicker/quickest
quicker, quickest
quicker, the quickest
Tallest is the superlative.
Quickly is an adverb The comparative form of quick is more quicker. The superlative form of quick is quickest.
quicker, quickest
Quickest.
quickest
quicker, the quickest
Quickest
quicker/quickest
quicker, quickest
quicker, the quickest
Rabbit
Sleep is a noun and does not have a superlative. Sleepy is an adjective and the superlative is "sleepiest."
The superlative for willing would be "most willing." There is no one-word superlative.